akko-mcp-trino

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Give your AI agents read-only access to Trino, and nothing more.

akko-mcp-trino is an MCP server for Trino. It lets an agent list catalogs, schemas and tables, describe a table, explain a query and run it, and it refuses every write it is sent: each statement is parsed, and a write anywhere in it is refused before Trino. By default every query runs as the user the agent acts for. The server verifies the user's token, issued for this server, and obtains from the identity provider a separate token for Trino (OAuth 2.0 Token Exchange): the user's own token never leaves the server. Trino's access control (OPA, Ranger, or Trino's own rules) then decides what that user may read. Results are bounded in rows and in time, and every call leaves one audit line.

Upgrading from 0.5? 0.6.0 changes the defaults: a verified caller is required, and the jwt mode exchanges the caller's token instead of passing it on. See MIGRATING.md.

Why

An agent that reads a lakehouse needs a small, predictable surface: a few tools whose descriptions a model understands, answers that never run away, and a guarantee that a prompt injection cannot turn a question into a DROP TABLE through it. This server is that surface, and nothing else. It does not decide access: Trino decides for each user with the rules it already has, or, in service mode, for the one identity you give it.

Highlights

• Read-only by construction, through this server. SQL is parsed into an AST and refused if a write appears anywhere in the tree, CTEs and subqueries included. Table functions (TABLE(...), such as a JDBC connector's system.query) and the system catalog are refused too, including through a name without a catalog when the session catalog is system. What a user may do in Trino by other means is Trino's rules: see What read-only covers.
• The user's own rights, safe by default. In jwt mode, the default, the server verifies the caller's token (issued for this server, never for Trino), exchanges it at the identity provider for a token whose audience is Trino (RFC 8693), and Trino runs the query as that user. The caller's token is never passed on. A request without a valid token is refused with 401.
• A fallback without token exchange. In impersonation mode the server authenticates to Trino as its own account (password or client certificate) and Trino runs the query as the verified caller, under an impersonation rule only that account has.
• One identity, only when named. In service mode every query runs as TRINO_USER. It is never chosen by default, and the server says so at start and to every host in its initialization instructions.
• Bounded by default. A row cap with a truncated flag (100), a time budget per query cancelled in Trino (60 s), a time budget per tool call (120 s).
• One audit line per call. Keyed by X-Request-Id, never the token, never the SQL text: who called which tool, with which outcome, for how long.
• Six tools, no more, annotated with what they can really do: execute_query is annotated read-only only while TRINO_READ_ONLY is true.
• A guarded door. Bearer tokens verified against any OIDC provider's JWKS (issuer, audience bound to this server, expiry, clock tolerance), a token issued for Trino refused, protected resource metadata (RFC 9728), a Host header filter.
• Built to be extended without being forked. Tool plugins and extensions are Python packages named at start: identity modes, guards at the door, audit fields, routes, tools. An extension can only refuse what the core allows, never widen it.
• Any MCP host, any model. Cursor, Claude Desktop, VS Code, the Python SDK… Mistral, or any OpenAI-compatible model through the example agent.
• Small and proven. 377 tests at 100 % line and branch coverage, including in-process suites on the real SDK for all three transports, a live run against Keycloak and Trino in CI (integration/), and a product-neutral guard.

Documentation

• How it works, end to end: akko-ai.com/en/docs/how-it-works (also en français).
• Guide, prerequisites, configuration, examples: akko-ai.com/docs/akko-mcp-trino (also in English) and akko-ai.com/docs/exemples.
• Reference, in this repository: this README, examples/, CHANGELOG.md, MIGRATING.md, CONTRIBUTING.md, SECURITY.md.

Contents

1. How it works
2. Compatibility
3. Prerequisites
4. Install and run
5. Connect an MCP host
6. Use it from an agent
7. The tools
8. What read-only covers
9. Extensions
10. What happens on a request
11. Configuration
12. Operations
13. Development
14. Design notes
15. Contributing
16. About AKKO

How it works

flowchart LR
    Host["MCP host<br/>(Cursor, Claude, VS Code, an agent)"]
    IdP["Identity provider<br/>(OIDC, JWKS, token exchange)"]
    Server["akko-mcp-trino"]
    Trino["Trino"]
    Policy["Policy engine<br/>(OPA, Ranger, built-in)"]
    Data[("Data sources")]

    Host -- "1. tool call + Bearer token<br/>(audience: this server)" --> Server
    Server -. "2. verify signature, issuer,<br/>audience, expiry (JWKS)" .-> IdP
    Server -. "3. exchange it for a token<br/>whose audience is Trino (RFC 8693)" .-> IdP
    Server -- "4. read-only SQL, with that token" --> Trino
    Trino -- "5. may this user read this?" --> Policy
    Trino -- "6. rows, as that user may read them" --> Server
    Server -- "7. result" --> Host
    Trino --> Data

The host calls a tool with the user's access token. The server verifies it (signature against the provider's JWKS, issuer, an audience naming this server, expiry) and refuses a request without a valid one with 401; a token issued for Trino is refused too. The server then checks the statement (read-only, identifiers, table functions, the system catalog) and runs it in Trino under the identity mode TRINO_IDENTITY_MODE names. Trino asks its policy engine and returns what that identity may read, bounded in rows and time.

Mode	Who Trino sees	How Trino knows	When to use it
jwt (default)	the caller	a token for Trino the server obtained by token exchange (RFC 8693); Trino verifies it with its JWT authenticator	the identity provider supports OAuth 2.0 Token Exchange (RFC 8693); tested with Keycloak 26
impersonation	the caller	the server's own account (password or client certificate) asks Trino to run the query as the caller; Trino allows it under an impersonation rule only that account has	the identity provider cannot exchange tokens
service	TRINO_USER, the same for every caller	a password, a client certificate, or nothing, locally	only when named: one identity for everyone, announced at start and to every host

The caller's own token never leaves the server, in any mode: the MCP authorization specification forbids passing it on ("token passthrough"). The caller's name always comes from their verified token, never from a header they wrote. Both modes that run as the caller refuse to start unless the door requires a valid token. An extension (see Extensions) may add other identity modes.

Compatibility

	Supported	Tested
Python	3.12, 3.13	3.12, 3.13 (CI)
Trino	351 and later; https with the JWT authenticator for jwt, with a password or certificate authenticator and impersonation rules for impersonation; http (local) or https for service	a recent release with the JWT and certificate authenticators, behind OPA and behind file-based rules, with row filters and column masks
Policy engines	OPA (trino-opa), Ranger (Trino plugin), Trino file-based access control	OPA and file-based rules, with row filters and column masks
Identity providers	any OIDC provider publishing a JWKS (the door); OAuth 2.0 Token Exchange, RFC 8693 (jwt mode)	Keycloak 26 (standard token exchange)
MCP	protocol negotiated by the official mcp SDK 2.2 (versions up to 2025-11-25); transports streamable-http, sse and stdio	all three, official SDK client, in CI
MCP hosts	remote: anything that sends a bearer header; local: any stdio host	Python SDK, the example agent
Models	any, the server never talks to a model	Mistral Small 3.2 through OpenRouter, driving the tools

Prerequisites

You need	Why	Notes
Python 3.12 or later	runtime	pip and a virtual environment
A reachable Trino coordinator	the engine	any recent version; https for jwt and impersonation, and whenever a secret is sent
An OIDC provider with a JWKS endpoint	the door	Keycloak, Entra ID, Okta, Dex… Tokens must carry iss, an aud naming this server, exp, and a subject (preferred_username or sub)
jwt: token exchange at the provider, and Trino's JWT authenticator	each user reads with their own rights	a confidential client for this server, allowed to exchange a token issued for it for one whose audience is Trino; http-server.authentication.type=JWT with the provider's JWKS and required-audience set to that audience
Or impersonation: an account for this server, and an impersonation rule	each user reads with their own rights, without token exchange	TRINO_USER with TRINO_PASSWORD or a client certificate; a Trino rule letting that account, and only it, impersonate users
Or service: one Trino identity	the rights of every caller	TRINO_USER, and TRINO_PASSWORD or a client certificate; give it read rights only on what every caller may read
A policy engine deciding for Trino	the governance	OPA (opa.policy.uri), Ranger, or Trino file-based rules
An MCP host	the client	Cursor, Claude Desktop, VS Code, or any client built on the mcp SDK

Optional: a Prometheus to scrape /metrics.

Install and run

pip install akko-mcp-trino        # or: pipx install akko-mcp-trino
uvx akko-mcp-trino --version      # run it without installing, the way most MCP hosts do

Or from source:

git clone https://github.com/AKKO-p/akko-mcp-trino.git
cd akko-mcp-trino
python -m venv .venv && source .venv/bin/activate
pip install -e .

The package installs a Python module (akko_mcp_trino) and a command (akko-mcp-trino); python -m akko_mcp_trino is the same entrypoint.

Point it at your Trino and your identity provider, then serve. The defaults are the safe ones: each query runs as the caller (jwt), and a request without a valid token is refused.

export TRINO_HOST=trino.example.internal
export TRINO_PORT=8443
export TRINO_HTTP_SCHEME=https          # required: a token never travels over http
export TRINO_CATALOG=iceberg

# The door: tokens issued for this server, verified against the provider's JWKS
export MCP_JWKS_URL=https://idp.example.com/realms/data/protocol/openid-connect/certs
export MCP_OIDC_ISSUER=https://idp.example.com/realms/data
export MCP_OIDC_AUDIENCE=akko-mcp        # the audience the provider gives tokens for this server
export MCP_RESOURCE_URL=https://mcp.example.com/mcp   # optional: this server's canonical URL

# A token for Trino, by token exchange (RFC 8693), never the caller's own
export TRINO_TOKEN_EXCHANGE_URL=https://idp.example.com/realms/data/protocol/openid-connect/token
export TRINO_TOKEN_EXCHANGE_CLIENT_ID=akko-mcp
export TRINO_TOKEN_EXCHANGE_CLIENT_SECRET=...
export TRINO_TOKEN_EXCHANGE_AUDIENCE=trino

python -m akko_mcp_trino

Before serving, akko-mcp-trino --check prints the effective configuration (never a secret), any warning, and exits with 2 if something would refuse to start; over stdio it checks that MCP_USER_TOKEN is present, not that it is valid (the real start verifies the token). Then:

INFO:__main__:serving transport=streamable-http port=3000 auth=True strict=True identity=jwt extensions=none

Check it is alive and can reach Trino:

curl -s localhost:3001/health   # {"status":"ok"}       never touches Trino
curl -s localhost:3001/ready    # {"status":"ready"}    jwt: Trino's /v1/info; impersonation and service: a bounded SELECT 1 as the server's account
curl -s localhost:3001/metrics  # Prometheus exposition

Each user with their own rights (jwt, the default)

The caller's token is issued for this server: its audience is MCP_OIDC_AUDIENCE (or MCP_RESOURCE_URL). The server exchanges it at the provider for a token whose audience is TRINO_TOKEN_EXCHANGE_AUDIENCE, keeps that token in memory until shortly before it expires, and sends it to Trino. A token whose audience is Trino's is refused at the door, and a configuration that would accept one refuses to start.

On the provider, give this server a confidential client allowed to exchange tokens, and make Trino's audience available to it. With Keycloak 26: enable Standard token exchange on the server's client, add an audience mapper for the Trino client to it, and have the clients of your MCP hosts put the server's client in the audience of the tokens they get (an audience mapper too). The integration/ folder holds such a realm, tested on every pull request.

On the Trino side, http-server.authentication.type=JWT, http-server.authentication.jwt.key-file set to the provider's JWKS URL, http-server.authentication.jwt.principal-field naming the same claim the server reads (preferred_username or sub), and required-issuer and required-audience pinning the token to your provider and to Trino's audience. Two users asking the same question then get the answers their own rights allow. /ready asks Trino's public /v1/info, since there is no identity of the server's own to query with.

Without token exchange (impersonation)

When the provider cannot exchange tokens, the server reaches Trino as its own account, and Trino runs each query as the verified caller:

export TRINO_IDENTITY_MODE=impersonation
export TRINO_USER=mcp-service
export TRINO_CLIENT_CERT=/certs/mcp-service.crt   # mTLS; or TRINO_PASSWORD over https
export TRINO_CLIENT_KEY=/certs/mcp-service.key

Trino must authenticate that account (the certificate or password authenticator, besides the one your users have) and allow it, and only it, to impersonate users. With file-based access control:

{"impersonation": [{"original_user": "mcp-service", "new_user": ".*", "allow": true}]}

Narrow new_user to the users the agents may act for. Nobody else may impersonate: a user who sends a header naming someone else is refused by Trino, and the server never takes the caller's name from a header, only from their verified token. Keep the account's credential as you would any service credential: whoever holds it can act as any user the rule allows.

One identity for every caller (service, only when named)

export TRINO_IDENTITY_MODE=service
export TRINO_USER=mcp-reader
export TRINO_PASSWORD=...               # or TRINO_CLIENT_CERT and TRINO_CLIENT_KEY; https only

Every query runs as TRINO_USER, whoever calls: give that identity the rights every caller of this server may have, no more, and read-only rights only. The server logs a warning at start, --check prints it, and every host receives it in the instructions of the MCP initialization. The door stays on by default; to run without one, locally, set MCP_AUTH_ENABLED=false and MCP_AUTH_REQUIRED=false too, and the warning says so.

Container

A Dockerfile ships with the repository (non-root, health check, OCI labels). Run it with the same environment variables, publishing ports 3000 (MCP) and 3001 (health).

Connect an MCP host

The host sends the user's access token from the identity provider, issued for this server; the server verifies it and names the caller in the audit line. A host that supports MCP authorization finds the provider through the protected resource metadata the server publishes when MCP_RESOURCE_URL is set.

Cursor, Claude Desktop, VS Code (mcp.json):

{
  "mcpServers": {
    "trino": {
      "url": "http://localhost:3000/mcp",
      "headers": {"Authorization": "Bearer <the user's access token>"}
    }
  }
}

From Python, with the official SDK:

import anyio
from mcp import ClientSession
from mcp.client.streamable_http import create_mcp_http_client, streamable_http_client


async def main(token: str):
    http = create_mcp_http_client(headers={"Authorization": f"Bearer {token}"})
    url = "http://localhost:3000/mcp"
    async with streamable_http_client(url, http_client=http) as (read, write):
        async with ClientSession(read, write) as session:
            await session.initialize()
            result = await session.call_tool("execute_query", {"sql": "SELECT 1"})
            print(result.content[0].text)


anyio.run(main, "<token>")

streamable-http (/mcp) is the default and what current hosts expect. Set MCP_TRANSPORT=sse for older hosts (/sse); the guard is the same on both.

Local hosts over stdio

Claude Desktop, Cursor and Mistral Vibe can launch the server themselves. There is no request then, so the caller comes from the environment: the user's own access token, issued for this server, verified exactly like a bearer header would be, and bound to the process. Strict mode, the default, refuses to start without it. Queries run as the user in jwt mode (the token is exchanged for one for Trino, as over http) and in impersonation mode, and as TRINO_USER in service mode.

{
  "mcpServers": {
    "trino": {
      "command": "uvx",
      "args": ["akko-mcp-trino"],
      "env": {
        "MCP_TRANSPORT": "stdio",
        "TRINO_HOST": "trino.example.internal", "TRINO_PORT": "8443", "TRINO_HTTP_SCHEME": "https",
        "MCP_JWKS_URL": "https://idp.example.com/realms/data/protocol/openid-connect/certs",
        "MCP_OIDC_ISSUER": "https://idp.example.com/realms/data",
        "MCP_OIDC_AUDIENCE": "akko-mcp",
        "TRINO_TOKEN_EXCHANGE_URL": "https://idp.example.com/realms/data/protocol/openid-connect/token",
        "TRINO_TOKEN_EXCHANGE_CLIENT_ID": "akko-mcp",
        "TRINO_TOKEN_EXCHANGE_CLIENT_SECRET": "...",
        "TRINO_TOKEN_EXCHANGE_AUDIENCE": "trino",
        "MCP_USER_TOKEN": "<the user's access token>"
      }
    }
  }
}

Use it from an agent

examples/agent.py is a complete agent in eighty lines: any OpenAI-compatible model (Mistral on La Plateforme, through OpenRouter or LiteLLM; or any other provider), the MCP tools, the user's token. The model never sees the token; the server receives it on every tool call and verifies it.

pip install akko-mcp-trino openai
export LLM_BASE_URL=https://api.mistral.ai/v1
export LLM_API_KEY=...
export LLM_MODEL=mistral-small-latest
export MCP_URL=http://localhost:3000/mcp
export USER_TOKEN=<the user's access token>
python examples/agent.py "Which catalogs can I see, and what is in them?"

The examples folder has the details.

The tools

Tool	Arguments	Returns
list_catalogs	none	{"catalogs": [...], "truncated": bool}: the catalogs Trino shows
list_schemas	catalog	{"schemas": [...], "truncated": bool}: schemas in that catalog
list_tables	catalog, schema	{"tables": [...], "truncated": bool}: tables and views in that schema
describe_table	catalog, schema, table, sample_rows (0 to 20)	columns, types, comments, truncated; a governed sample when asked; what an extension's describers add
explain_query	sql	{"plan": "..."}: how Trino would run a read-only statement, without running it
execute_query	sql, max_rows (optional, lower than the server cap)	{"columns": [...], "rows": [...], "row_count": n, "truncated": bool}

Every tool runs in Trino through the identity mode, the listing tools included: metadata is data, and Trino lists only what that identity may see. Every description is written for a model and says what the tool returns. The descriptions of describe_table and execute_query also say that a masked value or a missing row is the access policy, not an error to retry.

Every identifier is validated ([A-Za-z_][A-Za-z0-9_-]*) before it is placed in SQL. execute_query accepts any SQL Trino accepts, as long as it is a read: the statement is parsed into an AST and refused if it is more than one statement, or if an INSERT, UPDATE, DELETE, MERGE, CREATE, DROP, ALTER, GRANT, CALL or SET appears anywhere in the tree, including inside a CTE, a subquery, or the statement an EXPLAIN explains. EXPLAIN ANALYZE is refused: it executes what it explains. Table functions and the system catalog are refused, and so is any SHOW that names system. A name without a catalog is read in the session catalog (TRINO_CATALOG, system by default); when that is system, a table without a catalog is refused (a CTE is not a table), and only SHOW CATALOGS and a SHOW SCHEMAS, SHOW TABLES or SHOW COLUMNS whose FROM gives the full name, catalog included, get through. So set TRINO_CATALOG to a data catalog; the engine's policy must refuse system too, the guard being a second line.

Results are capped at TRINO_MAX_ROWS (100 by default, 1 at least): one row more is read, so truncated says whether the answer was cut, and the rest of the query is cancelled in Trino. Every listing says it too. With TRINO_QUERY_TIMEOUT_SECONDS (60 s by default), a query that runs longer is cancelled in Trino and the agent is told so. The budget is enforced by the server, not set as a session property: a policy engine that forbids users to set session properties would refuse every query otherwise. With MCP_CALL_TIMEOUT_SECONDS (120 s by default), a whole tool call has a time budget, every query it runs included: past it no query starts, the one running is cancelled (even when the budget ran out before Trino named it), and the agent gets {"error": "the tool call exceeded its time budget…"}, never what the call had gathered so far, nor an answer that came past the deadline. A plugin that calls its own backend bounds that request with akko_mcp_trino.audit.time_allowed(timeout): its own timeout, or what is left of the call's budget when that is shorter.

The defaults are chosen for an agent, not for a batch job. A question an agent asks should come back within a minute; a query that needs longer is usually a full scan the agent should narrow, and the error it gets says so. Two minutes per call leave room for a tool that runs two or three queries, without letting an agent's turn hang on one tool. Set either to 0 to remove the limit (the query then runs as long as Trino's own query.max-execution-time allows); --check prints both.

execute_query is annotated readOnlyHint: true only while TRINO_READ_ONLY is true. With TRINO_READ_ONLY=false, its annotations say it may write (readOnlyHint: false, destructiveHint: true) and so does its description, so that a host asks for the confirmation it would skip for a read-only tool. The five other tools only read, whatever the setting.

Errors come back to the agent as {"error": "..."} with Trino's whole message; a permission refusal from Trino is an ordinary error, not a crash. The audit line keeps only the error's code (see Audit).

Adding tools from another package

A product built on this server can add its own tools without forking it. A package registers a registrar (mcp, client) -> None, or (mcp, client, tools) -> None, under the entry-point group akko_mcp_trino.tools and the operator names it in MCP_TOOL_PLUGINS:

[project.entry-points."akko_mcp_trino.tools"]
my-tools = "my_package.tools:register"

from akko_mcp_trino.identity import current_subject


def register(mcp, client):
    @mcp.tool()
    def my_tool(text: str) -> str:
        return client.query("SELECT ...", user=current_subject())

Nothing is loaded that is not named, and an unknown name refuses to start. Tools added this way go through the same client, hence the same identity mode as the built-in ones, and every tool a registrar adds through mcp.tool() or mcp.add_tool() leaves the same audit line, with no change to the plugin. build_server(extra_tool_registrars=...) does the same from Python.

A registrar with a third argument receives the ToolContext: tools.tool(title, governed=..., open_world=...) registers a tool with its MCP annotations, tools.run(sql) queries Trino through the identity mode, tools.note(...) records what the call did (the SQL it ran, the tables, the rows, whether they were cut), and tools.add_describer(fn) adds to what describe_table answers:

import json


def register(mcp, client, tools):
    @tools.tool("Ask the data", governed=True, idempotent=False)
    def ask_data(question: str) -> str:
        answer = my_service.ask(question)  # runs its SQL through tools.run
        tools.note(sql=answer["sql"], tables=answer["tables"], rows=len(answer["rows"]))
        return json.dumps(answer)

What read-only covers

The read-only guard covers what passes through this server: every statement an agent sends is refused if a write appears anywhere in it, before Trino sees it. It is not a guarantee about what a user may do in Trino by other means.

In jwt and impersonation modes, Trino runs each query as the user, with the rights its policy gives that user. If that policy lets the user write, the user can still write through any other Trino client (the CLI, a notebook, a BI tool), with a token for Trino the provider gives them directly. The token the server obtains by exchange is held in memory and never returned to the agent or the host, but the user's own rights in Trino are what they are. In service mode the same holds for TRINO_USER, for whoever holds its credential.

For read-only end to end, make the engine hold the line too:

• service: give TRINO_USER read rights only. With file-based access control, {"catalogs": [{"user": "mcp-reader", "catalog": ".*", "allow": "read-only"}]}; with OPA or Ranger, a policy granting that identity SELECT and nothing else.
• impersonation: limit the impersonation rule to the users the agents may act for, and, if those users may write elsewhere, give the server's account no rights of its own beyond SELECT 1.
• jwt: let only this server's client obtain tokens for Trino's audience by exchange, so that a token the agent's host holds never opens Trino; and give the users reached through agents read-only rules on the catalogs agents may reach, in the policy engine. Trino applies the same rules to a query whatever client sent it, so the policy is where a user's rights are read-only for every path, this one included.

The guard stays a second line, not the only one: the engine's policy must refuse table functions and the system catalog too (see Design notes).

Extensions

A tool plugin adds tools. An extension may add more, around the core and never in place of it. A package registers a factory (config, env) -> Extension under the entry-point group akko_mcp_trino.extensions, and the operator names it in MCP_EXTENSIONS (comma-separated, in order):

[project.entry-points."akko_mcp_trino.extensions"]
my-extension = "my_package.extension:create"

from akko_mcp_trino.extensions import Extension, Refusal


class MyExtension(Extension):
    name = "my-extension"

    def after_auth(self, admission):
        if admission.principal is not None and admission.principal.subject.startswith("svc-"):
            return Refusal("service_accounts_refused", status=403)
        return None


def create(config, env):
    return MyExtension()

Nothing is loaded that is not named. An unknown name refuses to start, and so does a factory that raises ValueError on a setting it cannot serve; --check reports both. akko_mcp_trino.extensions.Extension is the base class: every hook does nothing, so an extension overrides only what it adds.

Hook	What it adds
check_lines()	lines --check prints, never a secret
identity_modes()	identity modes by TRINO_IDENTITY_MODE name, each an IdentityMode (describe, connection(user), ping); one named like a core mode (jwt, impersonation, service) replaces it
audiences()	token audiences accepted besides MCP_OIDC_AUDIENCE and MCP_RESOURCE_URL; never Trino's
before_auth(admission)	a refusal before the token is looked at, or None
after_auth(admission)	a refusal once the core has verified the token (or found none), or None
public_documents()	JSON documents served without a token, by request path; they take precedence over the core's
challenge(refusal)	the WWW-Authenticate value of a refusal; it takes precedence over the core's
routes()	Starlette routes added to the served app, behind the identity guard
wrap_audit(audit)	the audit sink the server writes to, given the one it would write to otherwise
client_tags()	client tags of a query run now (X-Trino-Client-Tags)
describe_table_doc()	text appended to the description of describe_table
tool_registrars()	tool registrars, called like a tool plugin's, before the plugins'

A guard answers a Refusal(reason, status=401, error="", headers={}, message=""): the reason goes into X-Reason and the body, error is the RFC 6750 code a challenge may carry, headers are added to the response (Retry-After), and message, when set, tells the client in the body what to do. It reads an Admission: the request headers, the token the request presented, the verified principal (None before authentication or without a token), stdio (true for the single admission of a stdio process); admission.bind(var, value) sets a context variable for the duration of the request, reset afterwards.

The rule: an extension can only refuse, never widen. Its guards run around the core's token verification, never instead of it; strict mode still refuses a request without a verified identity whatever a guard answers, and the read-only guard on SQL applies to every query. An identity mode decides who the server is for Trino, query by query (akko_mcp_trino.trino_client.resolve_identity picks the mode TRINO_IDENTITY_MODE names among the core's and the extensions', and refuses an unknown one: there is no fallback to service). A mode that sends Trino a token for the caller must obtain one for Trino, never forward the caller's: JwtIdentity.trino_token(bearer) is the hook. A plugin that calls its own backend for the caller reads the verified bearer with akko_mcp_trino.identity.current_bearer(), and must exchange it the same way rather than send it on. Trino decides what that identity may read.

What happens on a request

sequenceDiagram
    participant H as MCP host
    participant G as Guard (ASGI middleware)
    participant T as Tool
    participant Tr as Trino

    H->>G: POST /mcp  Authorization, X-Request-Id
    G->>G: request id: honoured or generated
    opt an extension's guard before the token
        G-->>H: its refusal  X-Reason
    end
    G->>G: verify JWT (JWKS, iss, aud = this server, exp) → Principal(subject)
    alt no valid token (none, forged, expired, issued for Trino)
        G-->>H: 401  X-Reason: unauthenticated, what to send
    end
    opt an extension's guard after the token
        G-->>H: its refusal  X-Reason
    end
    G->>T: Principal in a ContextVar
    T->>T: validate identifiers · refuse writes
    opt jwt mode, no valid exchanged token in memory
        T->>T: exchange the caller's token at the provider (RFC 8693)
    end
    T->>Tr: SQL as the caller (jwt: exchanged token; impersonation: server account), source
    Tr-->>T: rows (masked, filtered by the policy engine)
    T->>G: audit line {request_id, tool, subject, ok, error, duration_ms}
    G-->>H: result  X-Request-Id

Configuration

Everything is read from the environment. Nothing is hardcoded. An extension reads its own variables from the same environment.

Trino

Variable	Meaning	Default
TRINO_HOST, TRINO_PORT	the coordinator	localhost, 8080
TRINO_USER	the server's own Trino account: every query runs as it in service mode; in impersonation mode it authenticates and impersonates the caller	trino
TRINO_PASSWORD	its password, sent by Basic authentication; refused over http; --check says whether one is set, never which	none
TRINO_CLIENT_CERT, TRINO_CLIENT_KEY	a client certificate and its key (PEM paths) the account authenticates with instead (mTLS); https only	none
TRINO_CATALOG	session catalog, where a name without a catalog is read; set it to a data catalog (with system, such names are refused)	system
TRINO_READ_ONLY	refuse writes in execute_query	true
TRINO_MAX_ROWS	result cap, 1 at least; one more row is read to say whether the answer was truncated	100
TRINO_QUERY_TIMEOUT_SECONDS	time budget of one query: past it, the server cancels the query in Trino; 0 leaves the limit to Trino	60
MCP_CALL_TIMEOUT_SECONDS	time budget of one tool call, every query of the call included: past it, no query starts, the one running is cancelled and the agent gets an error; 0 sets none	120
TRINO_SOURCE	the source Trino records for every query (X-Trino-Source)	the server name
TRINO_HTTP_SCHEME	http or https; a password is never sent over http	http
TRINO_VERIFY	TLS verification: true, false, or a path to the CA bundle Trino's TLS chain is checked against	true
TRINO_REQUEST_TIMEOUT_SECONDS	per-request timeout on the Trino client	30
TRINO_IDENTITY_MODE	who the server is for Trino: jwt (every query as the caller, with a token for Trino obtained by token exchange), impersonation (every query as the caller, impersonated by TRINO_USER) or service (every query as TRINO_USER, announced as a warning); the first two need https and a door that requires a valid token; an extension may add others, and an unknown mode refuses to start	jwt
TRINO_TOKEN_EXCHANGE_URL	jwt: the provider's token endpoint (https only)	none (required in jwt)
TRINO_TOKEN_EXCHANGE_CLIENT_ID, TRINO_TOKEN_EXCHANGE_CLIENT_SECRET	jwt: this server's confidential client at the provider, sent by Basic authentication; --check never prints the secret	none (required in jwt)
TRINO_TOKEN_EXCHANGE_AUDIENCE	jwt: the audience of the token requested for Trino, the one Trino's required-audience names; never an audience this server accepts	none (required in jwt)
TRINO_TOKEN_EXCHANGE_SCOPE	jwt: scopes to request with it, space-separated	none
TRINO_TOKEN_EXCHANGE_VERIFY	TLS verification of the token endpoint: true, false, or a CA bundle path	true

Identity

Variable	Meaning	Default
MCP_AUTH_ENABLED	verify the callers' bearer tokens (the door)	true
MCP_AUTH_REQUIRED	refuse with 401 a request without a valid token; jwt and impersonation refuse to start without it	true
MCP_JWKS_URL	the provider's JWKS endpoint	none (required when auth is enabled)
MCP_OIDC_ISSUER	the issuer a token must carry	none
MCP_OIDC_AUDIENCE	the audience a token must carry: the one the provider gives tokens issued for this server (RFC 8707); never Trino's	none (this or MCP_RESOURCE_URL is required when auth is enabled)
MCP_RESOURCE_URL	this server's canonical URL, such as https://mcp.example.com/mcp: accepted as an audience, named in the protected resource metadata the server then publishes (RFC 9728) and in the challenge of a 401	none
MCP_JWT_LEEWAY_SECONDS	tolerance on exp/nbf/iat for clock drift between the issuer and this server	30
MCP_ALLOWED_HOSTS	Host header filter (the SDK's DNS rebinding protection): host or host:port entries, comma-separated, host:* for any port (the only wildcard); once the filter is on, a request that carries an Origin header is refused (403); empty serves any Host	none (off)

Auth enabled without a JWKS URL, or without an audience of this server's own, refuses to start: an authentication layer that cannot verify anything must not pretend to. So does a door that requires a token it cannot verify (MCP_AUTH_REQUIRED=true with MCP_AUTH_ENABLED=false).

Plugins and extensions

Variable	Meaning	Default
MCP_TOOL_PLUGINS	comma-separated names of registrars installed under the entry-point group akko_mcp_trino.tools	none
MCP_EXTENSIONS	comma-separated names of extensions installed under the entry-point group akko_mcp_trino.extensions	none

Serving

Variable	Meaning	Default
MCP_TRANSPORT	streamable-http, sse or stdio	streamable-http
MCP_PORT, MCP_HEALTH_PORT	listening ports	3000, 3001
MCP_SERVER_NAME	name announced to hosts	trino-mcp
MCP_USER_TOKEN	stdio only: the user's access token, verified like a bearer header	none (required in strict mode)

Operations

Refusals

Every refusal carries X-Reason and the request id, never the token. The core refuses with 401 unauthenticated a request without a valid token (none, forged, expired, or issued for another audience, Trino's included), and says in the body what to send:

{"error": "unauthenticated", "message": "this server requires a bearer token issued for it by the identity provider: send Authorization: Bearer <access token>"}

When MCP_RESOURCE_URL is set, the server publishes its protected resource metadata at /.well-known/oauth-protected-resource (and under the path of the URL, such as /.well-known/oauth-protected-resource/mcp), naming the resource and MCP_OIDC_ISSUER as its authorization server, and the 401 carries WWW-Authenticate: Bearer resource_metadata="…", as the MCP authorization specification asks. An extension's guards add their own reasons; its documents and challenges take precedence over the core's.

Warnings

A configuration that leaves something open is said three times: as a WARNING line at start, in --check, and to every MCP host in the instructions of the initialization. The core warns of service mode and of a door that does not require a valid token.

Audit

Every response of the MCP endpoint carries X-Request-Id. It is the one the gateway in front of the server sent, when it is a plain token (letters, digits, ., _, :, -, at most 128), or one the server generated. A tool call outside an HTTP request (stdio) gets its own id. Every tool call, a plugin's included, writes one JSON line to the mcp.audit logger keyed by that id:

{"request_id":"edge-42","tool":"execute_query","subject":"alice","ok":false,"error":"USER_ERROR:PERMISSION_DENIED","duration_ms":84}

With the default logging configuration, the line comes out prefixed with INFO:mcp.audit:; a collector that expects pure JSON strips that prefix.

Field	Meaning
request_id, tool, subject	which call, which tool, for whom; the line has no field that could hold the bearer or the SQL text
ok, error	the outcome; error is a code, never a message, because a message from Trino may quote a value read from a row (Cannot cast '<value>' to INT): Trino's error type and name for a Trino error (USER_ERROR:INVALID_CAST_ARGUMENT), the class of any other exception (TimeoutError, CallTimeout past the call's budget), the code a tool names for its own refusal (read_only, invalid_argument) or a plugin with note(error=...), else tool_error. The agent reads the whole message
duration_ms	how long the call took

What a call did (the SHA-256 of its SQL, the tables, the rows, whether they were cut) is kept in its record while it runs (akko_mcp_trino.audit.note); the core's line does not write it, an extension may (wrap_audit).

Health and metrics

/health on the health port never touches Trino, so a liveness probe cannot kill the server because Trino is slow. /ready asks the identity mode: in jwt mode Trino's public /v1/info; in impersonation and service modes, a bounded SELECT 1 as TRINO_USER, impersonating no one. /metrics exposes mcp_trino_queries_total, mcp_trino_query_errors_total and mcp_trino_query_duration_seconds.

Development

pip install -e ".[dev]"
ruff check akko_mcp_trino tests examples && ruff format akko_mcp_trino tests examples
ruff check akko_mcp_trino --select D100,D101,D102,D103,D105,D107   # every public name documented
mypy akko_mcp_trino           # the package ships py.typed and type-checks clean
pip-audit                     # no known vulnerability in the dependency tree
bash lint-vendor-neutral.sh   # fails if the package imports anything product-specific
pytest                        # 377 tests; line or branch coverage below 100 % fails the run
integration/run.sh            # live: Keycloak, Trino and three servers in Docker, then removed
python -m build && twine check dist/*
akko-mcp-trino --check        # effective configuration, no secrets; exit 2 if it would not start

tests/test_core_alone.py lists what the core holds (tools, modules, settings, audit fields) and fails the day something is added unlisted.

Every module in akko_mcp_trino/ has one responsibility and its tests, in tests/:

Module	Responsibility
config.py	read the environment, neutral defaults
auth.py	JWT verification against JWKS, Principal
identity.py	the verified caller in a ContextVar
middleware.py	the guard: token, request id, the extensions' guards and documents
extensions.py	the extension points and their loading
transport_security.py	the Host header filter (MCP_ALLOWED_HOSTS)
audit.py	the audit line, the request id, the record and the time budget of a call
sql_guard.py	identifier validation, read-only decision on the AST
tools.py, plugins.py	the six tools and the ToolContext, loading tool plugins
trino_client.py	the Trino connection, the identity modes (jwt, impersonation, service in the core) and the time budgets
token_exchange.py	OAuth 2.0 Token Exchange (RFC 8693): a token for Trino in exchange for the caller's
health.py, metrics.py	/health, /ready and /metrics; the Prometheus counters
server.py, app.py, __main__.py	assembly, transport, entrypoint and --check

The README is tested too: every variable listed here is read by config.py, and the defaults stated here are the defaults in the code.

Design notes

The guard is a pure ASGI middleware, not BaseHTTPMiddleware. The latter runs the downstream in a separate task and breaks ContextVar propagation: the verified caller would never reach the tools.

Mounting is transport-independent. One code path builds the transport app and mounts the guard, whatever the transport. The guard once lived only on the branch the default transport never took; a test now asserts it for both.

Every tool goes through the identity mode, not only execute_query. Listing catalogs, schemas and tables is reading metadata; a test walks every tool to check it reaches Trino the same way.

Read-only is decided on the AST, anywhere in the tree. A leading-keyword check lets WITH w AS (DELETE FROM t) SELECT 1 through. So did a root-node check, until a live adversarial proof caught it. The guard now walks the whole tree.

Table functions are refused. TABLE(pg.system.query(query => '...')) parses as a plain SELECT, yet it sends raw SQL to the source under the connector's own account, so the engine applies neither row filters nor column masks. The guard refuses every table function and the system catalog (which shows other users' SQL in system.runtime.queries). The engine policy must refuse them as well; the guard is a second line, not the only one.

No token passthrough. Up to 0.5, jwt mode sent Trino the caller's own token, once verified. The MCP authorization specification forbids it: a token issued for one service must not be sent on to another, or that service may trust a token that was never meant for it (the "confused deputy"). Since 0.6, the server accepts only tokens whose audience is its own, refuses a token issued for Trino, and obtains for Trino a token of its own by OAuth 2.0 Token Exchange (RFC 8693). Where the provider cannot exchange tokens, impersonation is the explicit fallback; it is never chosen in silence.

The verified identity, never one the caller names. The caller's name always comes from their verified token. A caller sending a header that names a Trino user changes nothing: the server builds its own request to Trino. A password, a token or a client certificate is never sent over plain http, and an identity mode the core does not know refuses to start rather than fall back.

Safe by default. Up to 0.5, the defaults ran every query as TRINO_USER and served a request without a token. Since 0.6, the default runs every query as the caller and refuses a request without a valid token; service mode and an open door are still possible, chosen by name, and announced as warnings. The row and time budgets have defaults too: unbounded was a choice nobody had made.

An extension can only refuse. Its guards run around the token verification, never instead of it, and the read-only guard applies whatever they answer.

The server does not decide access. Trino does, for each caller or for the configured identity. Putting policy in the server would duplicate, and eventually contradict, what the engine already enforces for every other client.

Contributing

Contributions are welcome: see CONTRIBUTING.md for the ground rules (tests first, 100 % coverage, product-neutral, fail closed) and SECURITY.md for reporting a vulnerability privately. Changes are tracked in CHANGELOG.md.

About AKKO

akko-mcp-trino is built and maintained by AKKO, a French project working on governed access for AI agents to enterprise data, in place, on the engines and identity providers organisations already run.

Maintained by: AKKO (contact@akko-ai.com) · Issues: github.com/AKKO-p/akko-mcp-trino/issues

License

Apache 2.0. See LICENSE.