fix: Identity JSON response header (#6326)

spec/controllers/microsoft_controller_spec.rb

@@ -6,7 +6,11 @@ describe '/.well-known/microsoft-identity-association.json', type: :request do
       with_modified_env AZURE_APP_ID: 'azure-application-client-id' do
         get '/.well-known/microsoft-identity-association.json'
         expect(response).to have_http_status(:success)
-        expect(response.body).to include '"applicationId":  "azure-application-client-id"'
+        expect(response.body).to include '"applicationId":"azure-application-client-id"'
+
+        content_length = { associatedApplications: [{ applicationId: 'azure-application-client-id' }] }.to_json.length
+
+        expect(response.headers['Content-Length']).to eq(content_length.to_s)
       end
     end
   end