auth-backend: deprecate tokenIssuer option of OAuthAdapter

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

.changeset/purple-boats-punch.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-auth-backend': patch
+---
+
+**DEPRECATION**: The `tokenIssuer` option for `OAuthAdapter` is no longer needed and has been deprecated.

plugins/auth-backend/src/lib/oauth/OAuthAdapter.ts

@@ -53,7 +53,8 @@ export type Options = {
   cookieDomain: string;
   cookiePath: string;
   appOrigin: string;
-  tokenIssuer: TokenIssuer;
+  /** @deprecated This option is no longer needed */
+  tokenIssuer?: TokenIssuer;
   isOriginAllowed: (origin: string) => boolean;
   callbackUrl: string;
 };