Document Cedar primary upstream provider selection

docs/toolhive/concepts/cedar-policies.mdx

@@ -567,20 +567,49 @@ groups or roles using the same `principal in THVGroup::"..."` syntax.
 ### How it works
 
 1. The embedded authorization server authenticates the user with your upstream
-   identity provider and issues a ToolHive JWT.
-2. The Cedar authorizer reads claims from the upstream token (not just the
-   ToolHive-issued JWT).
-3. Group claims are extracted and used to build `THVGroup` parent entities for
-   the principal.
+   identity provider, stores the upstream access token, and issues a ToolHive
+   JWT for the client.
+2. The authorizer resolves which token's claims to evaluate:
+   - When `primaryUpstreamProvider` is set, it reads claims from the named
+     upstream's stored access token.
+   - When `primaryUpstreamProvider` is unset and an embedded auth server is
+     configured, it reads claims from the first upstream provider declared on
+     the auth server.
+   - When `primaryUpstreamProvider` is unset and no embedded auth server is
+     configured, it reads claims from the bearer token on the original client
+     request.
+3. Group and role claims are extracted from the resolved claim source and used
+   to build `THVGroup` parent entities for the principal.
 4. Policies using `principal in THVGroup::"<group>"` evaluate correctly.
 
 :::note
 
-If the upstream token is opaque (not a JWT), the authorizer denies the request.
-There is no silent fallback to ToolHive-issued claims only.
+If the resolved upstream token is opaque (not a JWT), the authorizer denies the
+request. There is no silent fallback to the client request's claims.
 
 :::
 
+### How the upstream provider is chosen
+
+In Kubernetes, how you configure `primaryUpstreamProvider` depends on the
+resource type:
+
+- **VirtualMCPServer:** the embedded auth server can declare multiple upstream
+  providers. Set `incomingAuth.authzConfig.inline.primaryUpstreamProvider` on
+  the `VirtualMCPServer` to choose which upstream's access token Cedar
+  evaluates. When the field is empty, the operator defaults to the first entry
+  in `authServerConfig.upstreamProviders` and emits an
+  `AuthzUpstreamSelectionWarning` status condition naming the chosen provider.
+  See
+  [Cedar authorization claim source](../guides-vmcp/authentication.mdx#cedar-authorization-claim-source)
+  in the vMCP authentication guide for the override syntax and validation
+  behavior.
+- **MCPServer and MCPRemoteProxy:** the inline `primaryUpstreamProvider` field
+  is accepted but has no effect on these resources. Setting it surfaces an
+  `AuthzPrimaryUpstreamProviderIgnored` advisory status condition. The embedded
+  auth server for these resources runs through a referenced
+  `MCPExternalAuthConfig` and supports a single upstream provider.
+
 ## Policy evaluation and secure defaults
 
 Understanding how Cedar evaluates policies helps you write more effective and

docs/toolhive/guides-k8s/auth-k8s.mdx

@@ -849,6 +849,19 @@ membership. See
 [Upstream identity provider claims](../concepts/cedar-policies.mdx#upstream-identity-provider-claims)
 for details.
 
+:::note[`primaryUpstreamProvider` on MCPServer and MCPRemoteProxy]
+
+The embedded authorization server for `MCPServer` and `MCPRemoteProxy` resources
+is configured through a referenced `MCPExternalAuthConfig` and supports a single
+upstream provider, so there is no provider selection to make. The
+`primaryUpstreamProvider` field on the inline authz config is accepted on these
+resources but has no effect; setting it surfaces an
+`AuthzPrimaryUpstreamProviderIgnored` advisory status condition. Use a
+[`VirtualMCPServer`](../guides-vmcp/authentication.mdx#cedar-authorization-claim-source)
+when you need Cedar to choose between multiple upstream providers.
+
+:::
+
 **Step 1: Create authorization configuration**
 
 <BasicCedarConfig />

docs/toolhive/guides-vmcp/authentication.mdx

@@ -491,6 +491,66 @@ spec:
     # highlight-end
 ```
 
+### Cedar authorization claim source
+
+When you configure Cedar policies under `incomingAuth.authzConfig.inline`, the
+operator binds Cedar's claim source to one of the providers in
+`authServerConfig.upstreamProviders` so that group and role policies evaluate
+against upstream IDP claims rather than the ToolHive-issued JWT.
+
+By default, the operator selects the first entry in
+`authServerConfig.upstreamProviders`. With two or more upstreams declared the
+choice is ambiguous, so the operator additionally emits an
+`AuthzUpstreamSelectionWarning` status condition naming the chosen provider so
+you can verify the default matches your intent.
+
+To pin Cedar to a specific upstream, set `primaryUpstreamProvider` on the inline
+authz config:
+
+```yaml title="VirtualMCPServer resource"
+spec:
+  incomingAuth:
+    type: oidc
+    oidcConfigRef:
+      name: my-oidc-config
+      audience: https://mcp.example.com/mcp
+    authzConfig:
+      type: inline
+      inline:
+        # highlight-next-line
+        primaryUpstreamProvider: github
+        policies:
+          - 'permit(principal in THVGroup::"engineering", action, resource);'
+        entitiesJson: '[]'
+  authServerConfig:
+    issuer: https://auth.example.com
+    upstreamProviders:
+      - name: github
+        type: oauth2
+        oauth2Config: { ... }
+      - name: google
+        type: oidc
+        oidcConfig: { ... }
+```
+
+The value must match an entry in `authServerConfig.upstreamProviders`. Setting
+the field on a single-upstream config is allowed but redundant: the default
+already resolves to that upstream.
+
+Rejection behavior at admission:
+
+- **Name does not match a declared upstream:** the `VirtualMCPServer` is
+  rejected with `AuthServerConfigValidated=False` and `AuthzUpstreamUnknown`.
+  Cedar would otherwise deny every request at runtime, so the operator rejects
+  at admission instead.
+- **Field set without an embedded auth server:** the `VirtualMCPServer` is
+  rejected with `AuthzPrimaryProviderRequiresAuthServer`. Either remove the
+  field or configure `authServerConfig`.
+
+For background on how Cedar resolves claims from the upstream token versus the
+ToolHive-issued JWT, see
+[Upstream identity provider claims](../concepts/cedar-policies.mdx#upstream-identity-provider-claims).
+
 ### Session storage
 
 By default, upstream tokens are stored in memory and lost on pod restart. For