fix: use .text instead of .json for ALB key http call

.changeset/honest-jokes-rush.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-auth-backend': patch
+---
+
+Use .text instead of .json for ALB key response

plugins/auth-backend/src/providers/aws-alb/provider.test.ts

@@ -36,7 +36,7 @@ jest.mock('cross-fetch', () => ({
   __esModule: true,
   default: async () => {
     return {
-      json: async () => {
+      text: async () => {
         return mockKey();
       },
     };

plugins/auth-backend/src/providers/aws-alb/provider.ts

@@ -102,7 +102,7 @@ export class AwsAlbAuthProvider implements AuthProviderRouteHandlers {
     }
     const keyText: string = await fetch(
       `https://public-keys.auth.elb.${this.options.region}.amazonaws.com/${keyId}`,
-    ).then(response => response.json());
+    ).then(response => response.text());
     const keyValue = crypto.createPublicKey(keyText);
     this.keyCache.set(keyId, keyValue);
     return keyValue;