Mockingbird

Amazon Security Token Service

@crvouga/mockingbird-service-sts

Stateful Amazon Security Token Service emulator with AWS SDK wire compatibility and deterministic local controls.

Parity: Documented operations; LocalStack differential scenariosIdentity7 of 7 operationsIn-process fetchNode servermockingbird-sts
$
npm install -D @crvouga/mockingbird-service-sts
Source npm MarkdownAgent discoverySUPPORT.md

Playground

Requests go to the real emulator running in this tab. State persists across requests, and the journal shows what it received. A green dot marks operations whose sample succeeds as-is; others need ids from earlier responses.

Loads the real @crvouga/mockingbird-service-sts into this tab on first send
https://sts.us-east-1.amazonaws.com

Send a request to see the emulator's response.

Operations

7 of 7 operations in the vendored contract are emulated.

MethodPathOperationStatus
GET/AwsQuery
POST/AwsRpc
GET/{path}AwsRestGet
POST/{path}AwsRestPost
PUT/{path}AwsRestPut
PATCH/{path}AwsRestPatch
DELETE/{path}AwsRestDelete

Documentation

The package README, the same file that ships in the npm tarball.Edit on GitHub

Local emulators. Real API contracts. Part of Mockingbird.

Stateful local emulator of Amazon Security Token Service. ESM; Node 22+ or Bun 1.2+.

Usage

TypeScript
import { AssumeRoleCommand, GetCallerIdentityCommand, STSClient } from "@aws-sdk/client-sts"
import { createServer } from "@crvouga/mockingbird-service-sts/server"

// Test setup: start the emulator and point the SDK's endpoint at it.
const server = await createServer()
const sts = new STSClient({
  endpoint: server.url,
  region: "us-east-1",
  credentials: { accessKeyId: "fixture", secretAccessKey: "fixture" },
})

// Application code: the STS SDK calls it already makes.
const identity = await sts.send(new GetCallerIdentityCommand({}))
console.log(identity.Arn) // arn:aws:iam::000000000000:root
const assumed = await sts.send(
  new AssumeRoleCommand({
    RoleArn: "arn:aws:iam::000000000000:role/deploy",
    RoleSessionName: "ci",
  }),
)
console.log(assumed.AssumedRoleUser?.Arn) // arn:aws:sts::000000000000:assumed-role/deploy/ci

await server.close()

State lives in SQLite collections and participates in the shared runtime's namespace isolation, reset, timeline, clock, journal, metrics and fault controls. No AWS account is needed.

Implemented AWS operations: GetCallerIdentity, AssumeRole, GetSessionToken, GetFederationToken.

Operations outside this list fail explicitly. This package emulates API state, not AWS infrastructure, production quotas, billing, IAM enforcement, or provider consoles. Service-specific omissions and oracle evidence are recorded in the AWS coverage ledger.

Run bun run parity with LocalStack on http://127.0.0.1:4566; an unavailable oracle fails the run. No LocalStack run is recorded for this integration. The parity command is a bounded read-only SDK envelope probe, not proof of full vendor equivalence.

Install

Shell
bun add @crvouga/mockingbird-service-sts

API

  • StsAPI(options?): low-level AWS transport instance with fetch and reset.

  • createRuntime(options?): in-process Fetch API and shared state controls.

  • createServer(options?) from the /server entry: HTTP listener with url, runtime, and close().

  • document, operationIds, and supportedOperationIds: generated transport contract metadata.

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