Add OAuth2 API scope registration and enforcement

Register v1 API scopes in coredata, advertise them in OIDC discovery
and protected-resource metadata, show them on the consent screen, and
enforce scope-to-action mapping in the IAM Authorizer before policy
evaluation.

Signed-off-by: Ludovic Vielle <ludovic@probo.com>

pkg/iam/oauth2/protected_resource_metadata.go

@@ -0,0 +1,49 @@
+// Copyright (c) 2026 Probo Inc <hello@probo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+package oauth2
+
+import (
+	"slices"
+
+	"go.probo.inc/probo/pkg/coredata"
+	"go.probo.inc/probo/pkg/uri"
+)
+
+// ProtectedResourceMetadata represents the RFC 9728 protected resource metadata
+// document published at /.well-known/oauth-protected-resource.
+type ProtectedResourceMetadata struct {
+	Resource               uri.URI                `json:"resource"`
+	AuthorizationServers   []uri.URI              `json:"authorization_servers"`
+	BearerMethodsSupported []string               `json:"bearer_methods_supported"`
+	ScopesSupported        []coredata.OAuth2Scope `json:"scopes_supported"`
+}
+
+func NewProtectedResourceMetadata(
+	resource uri.URI,
+	authorizationServer uri.URI,
+	apiScopes []coredata.OAuth2Scope,
+) *ProtectedResourceMetadata {
+	return &ProtectedResourceMetadata{
+		Resource:             resource,
+		AuthorizationServers: []uri.URI{authorizationServer},
+		BearerMethodsSupported: []string{
+			"header",
+		},
+		ScopesSupported: slices.Concat(
+			[]coredata.OAuth2Scope{ScopeOpenID},
+			apiScopes,
+		),
+	}
+}