auth-backend: add forwarding of the SAML audience option

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

.changeset/selfish-bags-punch.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-auth-backend': patch
+---
+
+Added forwarding of the `audience` option for the SAML provider, making it possible to enable `audience` verification.

plugins/auth-backend/config.d.ts

@@ -75,6 +75,7 @@ export interface Config {
         logoutUrl?: string;
         issuer: string;
         cert: string;
+        audience?: string;
         privateKey?: string;
         authnContext?: string[];
         identifierFormat?: string;

plugins/auth-backend/src/providers/saml/provider.ts

@@ -125,6 +125,7 @@ export const createSamlProvider = (
       callbackUrl: `${globalConfig.baseUrl}/${providerId}/handler/frame`,
       entryPoint: config.getString('entryPoint'),
       logoutUrl: config.getOptionalString('logoutUrl'),
+      audience: config.getOptionalString('audience'),
       issuer: config.getString('issuer'),
       cert: config.getString('cert'),
       privateCert: config.getOptionalString('privateKey'),