Security and Access Control | Tigris Object Storage Documentation

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TAG is designed so your secret keys never leave your hands. This page explains how authentication, authorization, and credential handling work under the hood.

Setting up credentials

TAG needs two sets of credentials to operate:

Client credentials

Your application clients use their own Tigris credentials, signing requests with standard AWS SigV4. No changes are needed on the client side beyond pointing the endpoint URL at TAG. TAG never sees or stores client secret keys.

TAG's own credentials

Your application must provide TAG with credentials via environment variables:

export AWS_ACCESS_KEY_ID=<TAG's access key>

export AWS_SECRET_ACCESS_KEY=<TAG's secret key>

In transparent proxy mode (the default) these are TAG's own Tigris credentials, used only to sign proxy headers and perform background cache fetches — so read-only access to the cached buckets is sufficient, and TAG's access key must belong to the same Tigris organization as client access keys. In signing mode these credentials populate TAG's local credential store: clients authenticate with them and TAG re-signs every request with them, so they must carry whatever permissions clients need (read-only is not sufficient if clients write). See Credential handling by mode below.

Authentication

TAG operates in transparent proxy mode by default. In this mode, TAG forwards the client's original Authorization header to Tigris unchanged and adds cryptographically signed proxy headers (X-Tigris-Forwarded-Host, X-Tigris-Proxy-Access-Key, X-Tigris-Proxy-Timestamp, X-Tigris-Proxy-Signature) computed with TAG's own secret key. Tigris independently validates both the client's SigV4 signature and TAG's proxy signature in a single round-trip.

TAG never sees client secret keys, client credentials do not need to be stored anywhere other than on the client, and Tigris retains full control over authorization decisions.

Signing mode

Transparent proxy mode works only with Tigris (the X-Tigris-Proxy-* identity headers are meaningful only to Tigris). Set TAG_TRANSPARENT_PROXY=false (or upstream.transparent_proxy: false) to run signing mode instead, which works against any S3-compatible service — Tigris, AWS S3, MinIO, and others.

In signing mode TAG validates the incoming request signature against its local credential store, then re-signs the request for the upstream with the same access key and secret and streams it on. It re-signs (rather than forwarding the original signature) because it may transform the request — this is not identity translation; the upstream sees the same identity as the client. Because TAG must know the secret for every access key it serves, clients must authenticate with the credentials in TAG's store (by default the AWS_ACCESS_KEY_ID / AWS_SECRET_ACCESS_KEY pair).

Credential handling by mode

Local authentication

TAG doesn't call Tigris on every request. After your client's first request, TAG learns enough to validate signatures locally — so cache hits skip the network entirely.

How it works

On the first request, TAG learns your client's derived signing keys from Tigris. Every request after that is validated locally:

First request (key learning):
First Request (Key Learning)ClientTAGTigrisGET /bucket/key + AuthForward auth + proxy headers200 OK + X-Tigris-Proxy-Signing-KeysUnwrap & store derived keysGrant authz cache entry200 OK (signing key stripped)

Subsequent requests (local validation):
Subsequent Requests (Local Validation)ClientTAGGET /bucket/key + AuthValidate SigV4 locallyAuthz cache → grantedServe from cache200 OK · X-Cache: HIT

Access control flow

Here's the full decision tree TAG uses when a request arrives. Most paths end with a forward to Tigris — TAG only serves from cache when it has both a valid signature and a cached authorization grant:

Access Control Decision TreeRequest arrivesAuth header?missingForward to TigrismalformedReject 4xxpresentKey known?noForward, learn keysyesSigV4 valid?mismatchForward, re-learnvalidAuthz cache?missForward, re-authorizehitAuthValidatedServe from cache

Authorization lifecycle

Authorization decisions are cached per (accessKey, bucket) pair:

Authorization is strictly per-bucket. A client may have access to some buckets but not others, and TAG enforces this at the cache level.

Proxy header security

Preventing client injection

TAG overwrites any client-supplied proxy header values with TAG's own computed values. Clients cannot impersonate TAG or bypass proxy authentication.

Proxy signature computation

TAG computes the proxy signature using its own secret key. Only TAG (and Tigris, which knows TAG's key) can produce a valid proxy signature.

Endpoint validation

TAG validates the upstream endpoint at startup. In every mode it must be a well-formed absolute http:// or https:// URL with a host.

In transparent proxy mode (the default) the host must additionally be one of the following — the X-Tigris-Proxy-* identity headers are meaningful only to Tigris:

Any other host is a fatal startup error in transparent mode. Signing mode does not apply this allowlist — it can front any S3-compatible endpoint. TAG only ever forwards to the single operator-configured upstream (never a client-chosen one), so this is not an open proxy.

Error mapping