passsage 0.1.0

S3-backed caching proxy for mitmproxy (Pas³age = Passage + S3)

Passsage proxy

Passsage (or Pas³age to emphasize the backend choice) is named for the three S's in S3: it uses Amazon S3 or an S3-compatible object store to persist its cached objects.

A caching HTTP(S) proxy built on mitmproxy that stores responses in S3 storage. Useful for caching package repositories, API responses, and other HTTP traffic for improved performance and offline access.

Mitmproxy is used so Passsage can terminate TLS, inspect HTTP responses, and cache HTTPS content instead of blindly tunneling encrypted bytes. In explicit proxy mode, clients connect to the proxy and issue CONNECT requests for HTTPS; mitmproxy completes the upstream TLS handshake, generates a matching interception certificate signed by its local CA, and then speaks TLS with the client so it can read and cache the HTTP payloads. See https://docs.mitmproxy.org/stable/concepts/how-mitmproxy-works/ for the details.

Features

• S3-backed caching: Store cached responses in AWS S3 or S3-compatible storage (MinIO, LocalStack, etc.)
• Flexible caching policies: Configure how different URLs are cached
  • NoRefresh: Serve from cache without revalidation; fetch on miss
  • Standard: RFC 9111 compliant caching and revalidation
  • StaleIfError: Serve stale cache on upstream failure (4xx/5xx/timeout)
  • AlwaysUpstream: Always fetch from upstream, cache as fallback
  • NoCache: Pass through without caching
  • Default policy when no rule matches: Standard (override with --default-policy)
• Automatic failover: Serve cached content when upstream is unavailable
• Ban management: Temporarily ban unresponsive upstreams to avoid timeouts

Cache hits and misses

Passsage resolves each request to a cache policy, then uses S3 object metadata to decide whether to serve from cache or go upstream. In brief:

• Cache hits are served by rewriting the request to the S3 object (Cache-Status is set to hit and Age is derived from the stored timestamp).
• NoRefresh serves from cache immediately on a hit (no revalidation).
• Standard revalidates with an upstream HEAD when stale; if the cached ETag/Last-Modified matches, the cached object is served.
• StaleIfError serves stale cache on upstream failure, and Standard honors stale-if-error / stale-while-revalidate directives when present.
• AlwaysUpstream always fetches from upstream, even if cached.
• NoCache bypasses cache lookup for non-GET/HEAD or policy override.

Standard follows RFC 9111 HTTP caching semantics; stale-if-error and stale-while-revalidate are supported when present.

On cache misses, Passsage fetches from upstream and streams the response to the client. Responses are saved to S3 unless caching is disabled by policy or response headers (Cache-Control: no-store or private, or Vary: *). When Vary is present, cache keys include the Vary request headers so separate variants are stored and served.

Installation

pip install passsage

For development:

pip install -e ".[dev]"

Usage

Basic Usage

# Run with default settings (uses AWS S3)
passsage

# Run on a specific port (CLI or env var)
PASSSAGE_PORT=9090 passsage
passsage -p 9090

# Bind to a specific interface (CLI or env var)
PASSSAGE_HOST=127.0.0.1 passsage
passsage --bind 127.0.0.1

# Run with web interface
passsage --web

Client Setup (Certificate + Proxy Env Vars)

Passsage runs on mitmproxy, so clients must trust the mitmproxy CA certificate to avoid TLS errors. Mitmproxy exposes a magic domain, mitm.it, which serves the local certificate authority for download; see https://docs.mitmproxy.org/stable/concepts/certificates/. The examples below assume a localhost proxy; if you deploy Passsage on an intranet host, replace localhost:8080 with the proxy hostname/IP.

1. Start Passsage (example on localhost):

PASSSAGE_PORT=8080 passsage

2. Fetch the mitmproxy CA certificate from a client (as root, or with sudo):

curl -x http://localhost:${PASSSAGE_PORT} http://mitm.it/cert/pem -o /usr/local/share/ca-certificates/mitmproxy-ca-cert.crt
update-ca-certificates

Open the page and download the certificate for your OS or browser, or use the direct download above.

3. Install the certificate on the client:

• Linux (system trust store):

sudo cp ~/Downloads/mitmproxy-ca-cert.pem /usr/local/share/ca-certificates/mitmproxy-ca-cert.crt
sudo update-ca-certificates

• macOS:
  • Open the downloaded .pem in Keychain Access, add to "System", and set to "Always Trust".
• Windows:
  • Run mmc, add Certificates snap-in for "Computer account", then import the .pem into "Trusted Root Certification Authorities".

4. Set proxy environment variables on the client (some tools only honor lowercase):

export HTTP_PROXY="http://localhost:${PASSSAGE_PORT}"
export HTTPS_PROXY="http://localhost:${PASSSAGE_PORT}"
export NO_PROXY="localhost,127.0.0.1,::1"
export http_proxy="http://localhost:${PASSSAGE_PORT}"
export https_proxy="http://localhost:${PASSSAGE_PORT}"
export no_proxy="localhost,127.0.0.1,::1"
# Python uv requires this
export SSL_CERT_FILE=/etc/ssl/certs/ca-certificates.crt

You can also use per-command proxies:

curl -x http://localhost:${PASSSAGE_PORT} https://example.com/

With LocalStack (Local Development)

Start LocalStack:

docker run --rm -p 4566:4566 localstack/localstack

Create and configure the bucket:

# Using awslocal (pip install awscli-local)
awslocal s3 mb s3://proxy-cache
awslocal s3api put-bucket-policy --bucket proxy-cache --policy '{
  "Version": "2012-10-17",
  "Statement": [{
    "Sid": "PublicRead",
    "Effect": "Allow",
    "Principal": "*",
    "Action": ["s3:GetObject", "s3:HeadObject"],
    "Resource": "arn:aws:s3:::proxy-cache/*"
  }]
}'

Run Passsage:

passsage --s3-endpoint http://localhost:4566 --s3-bucket proxy-cache

Environment Variables

Variable	Description	Default
PASSSAGE_PORT	Proxy listen port	8080
PASSSAGE_HOST	Proxy bind host	0.0.0.0
S3_BUCKET	S3 bucket name for cache storage	364189071156-ds-proxy-us-west-2 (AWS) or proxy-cache (custom endpoint)
S3_ENDPOINT_URL	Custom S3 endpoint URL	None (uses AWS)

CLI Options

Usage: passsage [OPTIONS]

Options:
  -p, --port INTEGER              Port to listen on (default: 8080)
  -b, --bind TEXT                 Address to bind to (default: 0.0.0.0)
  --s3-bucket TEXT                S3 bucket for cache storage
  --s3-endpoint TEXT              S3 endpoint URL for S3-compatible services
  --test                          Run in test mode
  -m, --mode [regular|transparent|wireguard|upstream]
                                  Proxy mode (default: regular)
  -v, --verbose                   Enable verbose logging
  --health-port INTEGER           Health endpoint port (env: PASSAGE_HEALTH_PORT, 0 disables)
  --health-host TEXT              Health endpoint bind host (env: PASSAGE_HEALTH_HOST)
  --web                           Enable mitmproxy web interface
  --version                       Show the version and exit.
  --help                          Show this message and exit.

As a mitmproxy Script

You can also use Passsage directly as a mitmproxy script:

mitmproxy -s $(python -c "import passsage; print(passsage.get_proxy_path())")

Docker Development

The easiest way to develop and test Passsage is with Docker Compose, which sets up LocalStack S3 automatically.

Quick Start

# Production-like setup
docker compose up --build

# Development setup (with live code editing; mitmproxy reloads proxy on change)
docker compose -f docker-compose.yml -f docker-compose.dev.yml up --build

This starts:

• LocalStack S3 on port 4566 with pre-configured proxy-cache bucket
• Passsage proxy on port 8080
• Health endpoint on port 8082 (/health)

Development Workflow

1. Start dev environment: docker compose -f docker-compose.yml -f docker-compose.dev.yml up --build
2. Edit code in src/passsage/; mitmproxy reloads the proxy on change

See DEVELOPMENT.md for the full guide.

Building and Publishing

Build the Package

pip install build
python -m build

This creates dist/passsage-*.whl and dist/passsage-*.tar.gz.

Publish to PyPI

pip install twine

# Upload to Test PyPI first
twine upload --repository testpypi dist/*

# Upload to PyPI
twine upload dist/*

Publish to Private PyPI (CodeArtifact, etc.)

# Configure your repository in ~/.pypirc or use environment variables
twine upload --repository your-repo dist/*

Development

# Install with dev dependencies
pip install -e ".[dev]"

# Run tests
pytest

# Run linter
ruff check src/

# Format code
ruff format src/

Integration tests with Docker Compose

The integration suite expects a running proxy that allows X-Passsage-Policy overrides. Start Passsage with --allow-policy-header or set PASSAGE_ALLOW_POLICY_HEADER=1.

# Default port 8080 and health port 8082
PASSAGE_ALLOW_POLICY_HEADER=1 docker compose up --build

# Override the host port mappings
PROXY_PORT=9090 HEALTH_PORT=9092 PASSAGE_ALLOW_POLICY_HEADER=1 docker compose up --build

When the proxy runs in a container, the test server must be reachable by Passsage. On Linux, set the bind host and public host so the proxy can reach the test server:

export PASSAGE_TEST_SERVER_BIND_HOST=0.0.0.0
export PASSAGE_TEST_SERVER_HOST=host.docker.internal
export PROXY_URL=http://localhost:9090
pytest -m "not slow"

Health endpoint

Passsage starts a lightweight HTTP server for health checks on a separate port.

curl -f http://localhost:8082/health

Configure it via environment variables:

export PASSAGE_HEALTH_PORT=8082
export PASSAGE_HEALTH_HOST=0.0.0.0

Policy Overrides

You can override caching policies by pointing Passsage at a Python file. The file can define a RULES list, a get_rules() function, or a get_resolver() function. These are evaluated in this order:

1. get_resolver() -> return a PolicyResolver
2. get_rules() -> return a list of rules
3. RULES -> a list of rules

The file is loaded at runtime and does not need to be installed as a package.

Header-based policy override (client-side)

You can force a policy per request by sending the X-Passsage-Policy header. This override is disabled by default and must be enabled on the proxy.

passsage --allow-policy-header

curl -x http://localhost:8080 \
  -H "X-Passsage-Policy: NoRefresh" \
  http://example.com/data.csv

Supported values: NoRefresh, Standard, StaleIfError, AlwaysUpstream, NoCache.

Security note: this allows clients to bypass normal policy rules. A malicious or misconfigured client could force caching of sensitive responses or disable caching to increase upstream load. Only expose the proxy to trusted clients if you rely on header overrides.

Use a custom policy file

passsage --policy-file /path/to/policies.py

You can also set the environment variable:

export PASSAGE_POLICY_FILE=/path/to/policies.py
passsage

Example: simple rules list

# /path/to/policies.py
from passsage.policy import NoCache, NoRefresh, PathContainsRule, RegexRule

RULES = [
    PathContainsRule("/assets/", NoRefresh),
    RegexRule(r".*\\.csv$", NoRefresh),
    PathContainsRule("/api/private", NoCache),
]

Example: programmatic rules with defaults

# /path/to/policies.py
from passsage.default_policies import default_rules
from passsage.policy import AlwaysUpstream, PathContainsRule

def get_rules():
    rules = default_rules()
    rules.insert(0, PathContainsRule("/debug/", AlwaysUpstream))
    return rules

Example: full resolver with custom default policy

# /path/to/policies.py
from passsage.default_policies import default_rules
from passsage.policy import PolicyResolver, Standard

def get_resolver():
    return PolicyResolver(rules=default_rules(), default_policy=Standard)

Example: dynamic rule based on headers

# /path/to/policies.py
from passsage.policy import CallableRule, Context, NoCache, NoRefresh

def choose_policy(ctx: Context):
    for key, value in (ctx.headers or []):
        if key.lower() == "x-no-cache" and value == "1":
            return NoCache
    return NoRefresh

RULES = [
    CallableRule(choose_policy),
]

License

See LICENSE and NOTICE for copyright and attribution details.

MIT License - see LICENSE for details.