feat: implement oauth2 RFC 7009 token revocation endpoint (#20362)

Adds RFC 7009 token revocation endpoint

coderd/database/db2sdk/db2sdk.go

@@ -383,6 +383,9 @@ func OAuth2ProviderApp(accessURL *url.URL, dbApp database.OAuth2ProviderApp) cod
 			}).String(),
 			// We do not currently support DeviceAuth.
 			DeviceAuth: "",
+			TokenRevoke: accessURL.ResolveReference(&url.URL{
+				Path: "/oauth2/revoke",
+			}).String(),
 		},
 	}
 }

coderd/database/dbauthz/dbauthz.go

@@ -446,6 +446,34 @@ var (
 		Scope: rbac.ScopeAll,
 	}.WithCachedASTValue()
 
+	subjectSystemOAuth2 = rbac.Subject{
+		Type:         rbac.SubjectTypeSystemOAuth,
+		FriendlyName: "System OAuth2",
+		ID:           uuid.Nil.String(),
+		Roles: rbac.Roles([]rbac.Role{
+			{
+				Identifier:  rbac.RoleIdentifier{Name: "system-oauth2"},
+				DisplayName: "System OAuth2",
+				Site: rbac.Permissions(map[string][]policy.Action{
+					// OAuth2 resources - full CRUD permissions
+					rbac.ResourceOauth2App.Type:          rbac.ResourceOauth2App.AvailableActions(),
+					rbac.ResourceOauth2AppSecret.Type:    rbac.ResourceOauth2AppSecret.AvailableActions(),
+					rbac.ResourceOauth2AppCodeToken.Type: rbac.ResourceOauth2AppCodeToken.AvailableActions(),
+
+					// API key permissions needed for OAuth2 token revocation
+					rbac.ResourceApiKey.Type: {policy.ActionRead, policy.ActionDelete},
+
+					// Minimal read permissions that might be needed for OAuth2 operations
+					rbac.ResourceUser.Type:         {policy.ActionRead},
+					rbac.ResourceOrganization.Type: {policy.ActionRead},
+				}),
+				User:    []rbac.Permission{},
+				ByOrgID: map[string]rbac.OrgPermissions{},
+			},
+		}),
+		Scope: rbac.ScopeAll,
+	}.WithCachedASTValue()
+
 	subjectSystemReadProvisionerDaemons = rbac.Subject{
 		Type:         rbac.SubjectTypeSystemReadProvisionerDaemons,
 		FriendlyName: "Provisioner Daemons Reader",
@@ -643,6 +671,12 @@ func AsSystemRestricted(ctx context.Context) context.Context {
 	return As(ctx, subjectSystemRestricted)
 }
 
+// AsSystemOAuth2 returns a context with an actor that has permissions
+// required for OAuth2 provider operations (token revocation, device codes, registration).
+func AsSystemOAuth2(ctx context.Context) context.Context {
+	return As(ctx, subjectSystemOAuth2)
+}
+
 // AsSystemReadProvisionerDaemons returns a context with an actor that has permissions
 // to read provisioner daemons.
 func AsSystemReadProvisionerDaemons(ctx context.Context) context.Context {