.NET SDK - Workload Identity Federation

For deployments that prefer not to manage static API keys, the .NET SDK can authenticate via Workload Identity Federation (WIF). The SDK fetches a workload OIDC token from the running environment, exchanges it for a Nexus session JWT, and uses Authorization: Bearer <jwt> on every subsequent API call. WIF is opt-in. When NexusConfig.Wif is null (the default), the SDK falls back to the static ApiKey flow and behaves exactly as in v0.1.0.

Enabling

await using var client = await NexusClient.CreateAsync(new NexusConfig
{
    BaseUrl = "https://blue-ocean-a5rx7.westyx.dev",
    Wif = new WIFConfig
    {
        Enabled  = true,
        Provider = WIFProvider.Auto, // default - auto-detect from env
    },
});

ApiKey becomes optional when WIF is enabled.

Security note (v0.9.0): BaseUrl must use https:// - NexusClient.CreateAsync refuses plain-http endpoints (loopback/localhost excepted for development), since credentials travel on every request.

Supported providers

When Provider is WIFProvider.Auto the SDK probes the environment in this order and picks the first provider whose credential material is actually present (v0.9.0 - file stats + live metadata probes, ~1 s timeout; earlier versions keyed on environment variables absent on real cloud nodes):

Provider constant	Auto-detect signal	Credential
`WIFProvider.Kubernetes`	`/var/run/secrets/kubernetes.io/serviceaccount/token` exists	reads the projected service-account token file (rotated by kubelet)
`WIFProvider.AWS`	`AWS_WEB_IDENTITY_TOKEN_FILE` set and the file exists (EKS IRSA)	reads the IRSA token file at that path
`WIFProvider.Azure` (Workload Identity)	`AZURE_FEDERATED_TOKEN_FILE` set and the file exists (AKS)	reads the projected federated token file
`WIFProvider.GCP`	`metadata.google.internal` reachable (live probe)	GETs `metadata.google.internal/computeMetadata/v1/.../identity?audience=<aud>` with `Metadata-Flavor: Google`
`WIFProvider.Azure` (IMDS)	`169.254.169.254/metadata` reachable (live probe)	GETs an Azure IMDS managed-identity token - requires `Audience = "api://<client-id>"` (your app registration’s Application ID URI; the generic default is refused because Azure AD rejects it)
`WIFProvider.AWSIAM`	not auto-detected - select explicitly (resolvable AWS credentials alone, e.g. a dev laptop’s `~/.aws/credentials`, are too weak a signal)	SigV4-signs an STS `GetCallerIdentity` request (never sent to AWS) that Nexus replays to prove your IAM role - works on ECS/Fargate, Lambda, and plain EC2

The OIDC providers use only the BCL HTTP client; aws_iam additionally uses AWSSDK.Core for the credential/region chain. You can also pin a specific provider:

Wif = new WIFConfig
{
    Enabled  = true,
    Provider = WIFProvider.Kubernetes,
}

AWS IAM (non-EKS AWS compute)

ECS/Fargate tasks, Lambda functions, and plain EC2 instances have IAM credentials but no OIDC token, so the OIDC providers above cannot serve them. The aws_iam provider closes this gap:

Wif = new WIFConfig
{
    Enabled  = true,
    Provider = WIFProvider.AWSIAM,
    // AWSRegion = "eu-central-1", // optional - defaults to the standard AWS region chain (env, config file, EC2 IMDS)
}

How it works:

The SDK SigV4-signs an STS GetCallerIdentity request using the standard AWS credential chain (task role, instance profile, env). The request is never sent to AWS by the SDK.
The signed request (headers + body) is posted to /v1/auth/token-exchange as {"provider":"aws_iam","aws_sts_request":...}.
Nexus replays it against a pinned STS endpoint; AWS answers with the caller’s IAM identity, which Nexus matches against an aws_iam trust policy (subject = the assumed-role ARN, normalized to arn:aws:iam::<account>:role/<name>).

Nothing else to configure: the SDK signs your service’s own host (the BaseUrl host) into the X-Nexus-Server-ID header inside the SigV4 signature, and Nexus verifies it against the host the exchange request actually arrived on. A captured signed request is therefore valid for that ONE service only - it cannot be replayed against any other service or deployment. aws_iam is never auto-detected - select it explicitly.

Custom `TokenSource`

Provide a TokenSourceFunc to bypass auto-detection entirely.

Wif = new WIFConfig
{
    Enabled = true,
    TokenSource = ct => ReadMyOidcTokenAsync(ct),
}

When TokenSource is non-null it takes precedence over Provider.

Audience

GCP and Azure require an audience claim when issuing the OIDC token:

Wif = new WIFConfig
{
    Enabled  = true,
    Provider = WIFProvider.GCP,
    Audience = "westyx-nexus",
}

The default is "westyx-nexus" if unset. Azure IMDS is the exception: the generic default is refused with a clear error, because Azure AD rejects it as a resource. On the IMDS path (plain VM / App Service - no federated token file) you MUST set Audience to your app registration’s Application ID URI (api://<client-id>). On AKS with Azure Workload Identity the projected federated token file ($AZURE_FEDERATED_TOKEN_FILE) is preferred automatically and no Audience is needed.

Token exchange flow

OIDC token fetch - WIFConfig.TokenSource (or the auto-detected built-in equivalent) returns a workload-identity JWT.

Token exchange - the SDK POSTs {"oidc_token": "<jwt>"} to /v1/auth/token-exchange. The backend validates the OIDC issuer/signature and returns:

{
  "session_token":  "<jwt>",
  "token_type":     "Bearer",
  "expires_in":     3600,
  "service_kind":   "backend",
  "wif_provider":   "kubernetes"
}

Bearer auth on subsequent calls - every /v1/* request carries Authorization: Bearer <session_token>.
Auto-refresh - ~60 s before expiry the SDK silently re-runs steps 1-2 from a background Task. The active SSE stream is not interrupted.
auth_expiring event - when the server emits this control event over SSE, the SDK pre-emptively refreshes the session before the server force-closes the stream.

Split HTTP clients

The SDK uses two separate HttpClient instances - one for short requests (/sync, /token-exchange, Timeout = 10s) and one for the long-lived SSE stream (Timeout = Timeout.InfiniteTimeSpan). This prevents a consumer-supplied short timeout from killing the stream after a few seconds. If you pass your own HttpClient via NexusConfig.HttpClient, the SDK clones it for the stream side and overrides the timeout - your sync client is untouched.

Project-level vs service-level trust policies

The Nexus backend supports trust policies at two scopes:

Scope	What it covers	Recommended for
Project-level	All services in the project share one policy	Most teams - no per-service cloud identity needed
Service-level	A specific policy bound to one service only	High-security services (payments, PII)

A project-level trust policy is less restrictive than a service-level one. Any workload that satisfies the policy can connect to any service in the project by targeting its BaseUrl. For services handling sensitive data (payments, credentials, PII) consider a dedicated service-level trust policy.

Overview

Backend SDKs

Browser SDKs

OpenFeature Providers

.NET SDK - Workload Identity Federation

Enabling

Supported providers

AWS IAM (non-EKS AWS compute)

Custom `TokenSource`

Audience

Token exchange flow

Split HTTP clients

Project-level vs service-level trust policies

​Enabling

​Supported providers

​AWS IAM (non-EKS AWS compute)

​Custom TokenSource

​Audience

​Token exchange flow

​Split HTTP clients

​Project-level vs service-level trust policies

Enabling

Supported providers

AWS IAM (non-EKS AWS compute)

Custom `TokenSource`

Audience

Token exchange flow

Split HTTP clients

Project-level vs service-level trust policies