Add custom authorization header for OAuth2.0 strategy

Signed-off-by: Sonali Mishra <sonali.priyam@gmail.com>
Signed-off-by: Sonali Mishra <sonali.mishra@grabtaxi.com>

.changeset/thin-poems-watch.md

@@ -0,0 +1,9 @@
+---
+'@backstage/plugin-auth-backend': patch
+---
+
+---
+
+## '@backstage/plugin-auth-backend': patch
+
+Added custom OAuth2.0 authorization header for generic oauth2 provider.

plugins/auth-backend/src/providers/oauth2/provider.ts

@@ -85,6 +85,12 @@ export class OAuth2AuthProvider implements OAuthHandlers {
         tokenURL: options.tokenUrl,
         passReqToCallback: false as true,
         scope: options.scope,
+        customHeaders: {
+          Authorization: `Basic ${this.encodeClientCredentials(
+            options.clientId,
+            options.clientSecret,
+          )}`,
+        },
       },
       (
         accessToken: any,
@@ -187,6 +193,10 @@ export class OAuth2AuthProvider implements OAuthHandlers {
 
     return response;
   }
+
+  encodeClientCredentials(clientID: string, clientSecret: string): string {
+    return Buffer.from(`${clientID}:${clientSecret}`).toString('base64');
+  }
 }
 
 export const oAuth2DefaultSignInResolver: SignInResolver<OAuthResult> = async (