Crate Layout

The project is organized as a Cargo workspace with libraries (traits and logic) and example runtimes (executable targets).

crates/
├── core/  (multistore)                 # Runtime-agnostic: traits, S3 parsing, SigV4, registries
├── metering/ (multistore-metering)     # Usage metering and quota enforcement middleware
├── sts/   (multistore-sts)             # OIDC/STS token exchange (AssumeRoleWithWebIdentity)
└── oidc-provider/                      # Outbound OIDC provider (JWT signing, JWKS, exchange)

examples/
├── server/ (multistore-server)         # Tokio/Hyper for container deployments
├── lambda/ (multistore-lambda)         # AWS Lambda runtime
└── cf-workers/ (multistore-cf-workers) # Cloudflare Workers for edge deployments

Crate Responsibilities

multistore

The runtime-agnostic core. Contains:

• ProxyGateway — Router-based dispatch + S3 parsing + identity resolution + two-phase request dispatch (handle_request() → GatewayResponse)
• Router — Path-based route matching via matchit for efficient pre-dispatch
• RouteHandler trait — Pluggable request interception
• Middleware trait — Composable post-auth middleware for dispatch, with after_dispatch for post-response observation
• Forwarder trait — Runtime-provided HTTP transport for backend forwarding; the core orchestrates the call so middleware can observe response metadata
• BucketRegistry trait — Bucket lookup, authorization, and listing
• CredentialRegistry trait — Credential and role storage
• ProxyBackend trait — Runtime abstraction for store/signer/raw HTTP
• S3 request parsing, XML response building, list prefix rewriting
• SigV4 signature verification
• Sealed session token encryption/decryption
• Type definitions (BucketConfig, RoleConfig, AccessScope, etc.)

Feature flags:

• azure — Azure Blob Storage support
• gcp — Google Cloud Storage support

multistore-metering

Usage metering and quota enforcement middleware:

• MeteringMiddleware<Q, U> — Pre-dispatch quota checking + post-dispatch usage recording via the Middleware trait
• QuotaChecker trait — Pre-dispatch quota enforcement; return Err(QuotaExceeded) to reject with HTTP 429
• UsageRecorder trait — Post-dispatch operation recording for usage tracking
• UsageEvent — Operation metadata passed to the recorder (identity, operation, bytes, status)
• NoopQuotaChecker / NoopRecorder — Convenience no-op implementations for when only one side is needed

multistore-sts

OIDC token exchange implementing AssumeRoleWithWebIdentity:

• StsRouterExt — registers a closure that intercepts STS requests on the Router
• JWT decoding and validation (RS256)
• JWKS fetching and caching
• Trust policy evaluation (issuer, audience, subject conditions)
• Temporary credential minting with scope template variables

multistore-oidc-provider

Outbound OIDC identity provider for backend authentication:

• OidcRouterExt — registers closures for .well-known discovery endpoints on the Router
• RSA JWT signing (JwtSigner)
• JWKS endpoint serving
• OpenID Connect discovery document
• AWS credential exchange (AwsBackendAuth middleware)
• Credential caching

multistore-server

The native server runtime (in examples/server/):

• Tokio/Hyper HTTP server
• ServerBackend implementing ProxyBackend with reqwest
• Streaming via hyper Incoming bodies and reqwest bytes_stream()
• Wires ProxyGateway with a Router (OIDC discovery + STS routes)
• CLI argument parsing (--config, --listen, --domain, --sts-config)

multistore-cf-workers

The Cloudflare Workers WASM runtime (in examples/cf-workers/):

• WorkerBackend implementing ProxyBackend with web_sys::fetch
• WorkerForwarder implementing Forwarder with the Fetch API (zero-copy ReadableStream)
• FetchConnector bridging object_store HTTP to Workers Fetch API
• BandwidthMeter Durable Object — per-(bucket, identity) sliding-window byte counter
• DoBandwidthMeter implementing QuotaChecker + UsageRecorder via the BandwidthMeter DO
• CfRateLimiter middleware for request-rate limiting via CF Rate Limiting API
• Config loading from env vars (PROXY_CONFIG, BANDWIDTH_QUOTAS)

WARNING

This crate is excluded from the workspace default-members because WASM types are !Send and won't compile on native targets. Always build with --target wasm32-unknown-unknown.

Dependency Flow

Libraries define trait abstractions. Runtimes implement ProxyBackend and Forwarder with platform-native primitives, build a Router with extension traits, and handle the two-variant GatewayResponse.