pymayfly

Identity-Per-Transaction for regulated data pipelines.

Like a mayfly, these credentials live for exactly one transaction.

The Problem

Most enterprise "zero trust" implementations authenticate once and trust indefinitely. A single compromised credential — a leaked IAM role, a stolen service account key, a reused session token — exposes your entire data lake for hours or days.

The Solution

Identity-Per-Transaction (IPT) issues credentials scoped to exactly one resource for exactly one transaction. A compromised credential exposes one object. When that object is deleted post-processing, the credential points at nothing for the remainder of its TTL.

Traditional model:   compromised key → entire data lake
IPT model:           compromised key → single S3 object key (now deleted)

Install

pip install pymayfly[aws]     # AWS STS backend (FedRAMP-suitable)
pip install pymayfly[azure]   # Azure Blob backend (AAD User Delegation SAS)
pip install pymayfly[gcp]     # GCS backend (impersonation + downscoped tokens)
pip install pymayfly          # core only — bring your own provider

Quickstart

Decorator (AWS Lambda)

import boto3

from pymayfly import IPTEnforcer, AWSSTSBroker, FileAuditLedger

enforcer = IPTEnforcer(
    broker=AWSSTSBroker(role_arn="arn:aws:iam::123456789012:role/IPTProcessor"),
    ledger=FileAuditLedger("/var/log/mayfly/audit.jsonl"),
)

@enforcer.protect(
    resource_from=lambda e: (
        f"arn:aws:s3:::{e['Records'][0]['s3']['bucket']['name']}"
        f"/{e['Records'][0]['s3']['object']['key']}"
    ),
    action="read",
)
def handler(event, context, *, creds):
    s3 = boto3.client(
        "s3",
        aws_access_key_id=creds.token["AccessKeyId"],
        aws_secret_access_key=creds.token["SecretAccessKey"],
        aws_session_token=creds.token["SessionToken"],
    )
    record = event["Records"][0]
    bucket = record["s3"]["bucket"]["name"]
    key = record["s3"]["object"]["key"]

    data = s3.get_object(Bucket=bucket, Key=key)
    # process, de-identify, write to clean zone
    # delete source object → credential now points at nothing

Context Manager

from pymayfly import transaction_scope, AWSSTSBroker

broker = AWSSTSBroker(role_arn="arn:aws:iam::123456789012:role/IPTProcessor")

with transaction_scope(
    broker,
    resource="arn:aws:s3:::bucket/patient-001.parquet",
    action="read",
) as creds:
    # creds scoped to exactly this object
    process(creds)
# creds revoked (or expired) here

Providers

Security Properties

For a 1M-object data lake: blast radius reduced by 99.999%.

Implementing a Custom Provider

Subclass IdentityBroker and implement three methods:

from pymayfly import IdentityBroker, EphemeralCredential

class MyBroker(IdentityBroker):
    def issue(self, transaction_id, resource, action) -> EphemeralCredential:
        ...
    def revoke(self, credential) -> None:
        ...
    def blast_radius(self, credential) -> str:
        ...

See docs/providers.md for a provider walkthrough and pymayfly/providers/aws_sts.py for a complete implementation.

Research

This library implements the Identity-Per-Transaction protocol described in:

McKinnon, T. (2026). Zero-Trust Data Engineering: A Reference Architecture for Serverless, FedRAMP-High Healthcare Pipelines. IEEE BigDataSecurity 2026. TechRxiv preprint

Contributing

Issues and PRs welcome. See CONTRIBUTING.md.

Provider contributions especially encouraged — if you implement a Vault or Supabase backend, open a PR. Use the new provider issue template.

License

Apache 2.0. See LICENSE.

Built and maintained by Deterministic Systems Lab.