backend-common: add allowDisabledTokenManager option for ServerTokenManager

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

.changeset/smooth-garlics-behave.md

@@ -0,0 +1,5 @@
+---
+'@backstage/backend-common': patch
+---
+
+Added option to `ServerTokenManager.fromConfig` that allows it to be instantiated in production without any configured keys.

packages/backend-common/api-report.md

@@ -772,7 +772,7 @@ export class ServerTokenManager implements TokenManager {
   static fromConfig(
     config: Config,
     options: ServerTokenManagerOptions,
-  ): ServerTokenManager;
+  ): TokenManager;
   // (undocumented)
   getToken(): Promise<{
     token: string;
@@ -782,6 +782,7 @@ export class ServerTokenManager implements TokenManager {
 
 // @public
 export interface ServerTokenManagerOptions {
+  allowDisabledTokenManager?: boolean;
   logger: LoggerService;
 }
 

packages/backend-common/src/tokens/ServerTokenManager.test.ts

@@ -301,6 +301,20 @@ describe('ServerTokenManager', () => {
           ),
         ).toThrow();
       });
+
+      it('should throw errors when disabled', async () => {
+        const manager = ServerTokenManager.fromConfig(new ConfigReader({}), {
+          logger,
+          allowDisabledTokenManager: true,
+        });
+
+        await expect(manager.getToken()).rejects.toThrow(
+          'Unable to generate legacy token',
+        );
+        await expect(manager.authenticate('nah')).rejects.toThrow(
+          'Unable to authenticate legacy token',
+        );
+      });
     });
 
     describe('NODE_ENV === development', () => {

packages/backend-common/src/tokens/ServerTokenManager.ts

@@ -40,6 +40,23 @@ class NoopTokenManager implements TokenManager {
   async authenticate() {}
 }
 
+/**
+ * A token manager that throws an error when trying to generate or authenticate tokens.
+ */
+class DisabledTokenManager implements TokenManager {
+  async getToken(): Promise<{ token: string }> {
+    throw new Error(
+      "Unable to generate legacy token, no legacy keys are configured in 'backend.auth.keys' or 'backend.auth.externalAccess'",
+    );
+  }
+
+  async authenticate() {
+    throw new AuthenticationError(
+      "Unable to authenticate legacy token, no legacy keys are configured in 'backend.auth.keys' or 'backend.auth.externalAccess'",
+    );
+  }
+}
+
 /**
  * Options for {@link ServerTokenManager}.
  *
@@ -50,6 +67,11 @@ export interface ServerTokenManagerOptions {
    * The logger to use.
    */
   logger: LoggerService;
+
+  /**
+   * Whether to disable the token manager if no keys are configured.
+   */
+  allowDisabledTokenManager?: boolean;
 }
 
 /**
@@ -73,7 +95,10 @@ export class ServerTokenManager implements TokenManager {
     return new NoopTokenManager();
   }
 
-  static fromConfig(config: Config, options: ServerTokenManagerOptions) {
+  static fromConfig(
+    config: Config,
+    options: ServerTokenManagerOptions,
+  ): TokenManager {
     const oldSecrets = config
       .getOptionalConfigArray('backend.auth.keys')
       ?.map(c => c.getString('secret'));
@@ -87,6 +112,14 @@ export class ServerTokenManager implements TokenManager {
       return new ServerTokenManager(secrets, options);
     }
 
+    // When using the new backend system with new auth services we instead rely
+    // on the new plugin auth and external access configurations. If no legacy
+    // keys are configured we disable the token manager completely, rather than
+    // requiring users to configure legacy keys.
+    if (options.allowDisabledTokenManager) {
+      return new DisabledTokenManager();
+    }
+
     if (process.env.NODE_ENV !== 'development') {
       throw new Error(
         'You must configure at least one key in backend.auth.keys for production.',