authentication/LegacyAuthQuickstart/AuthenticationExample/MainViewController.m [265:290]:
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                completion:^(FIRAuthCredential *_Nullable credential, NSError *_Nullable error) {
              [self showSpinner:^{
                 if (error) {
                   [self hideSpinner:^{
                     [self showMessagePrompt:error.localizedDescription];
                     return;
                   }];
                 }
                if (credential) {
                  [[FIRAuth auth] signInWithCredential:credential
                                            completion:^(FIRAuthDataResult *_Nullable authResult,
                                                         NSError *_Nullable error) {
                    [self hideSpinner:^{
                      if (error) {
                        [self showMessagePrompt:error.localizedDescription];
                        return;
                      }
                    }];
                  }];
                }
              }];
            }];
            // [END firebase_auth_twitter]
         }];
      }
        break;
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authentication/LegacyAuthQuickstart/AuthenticationExample/MainViewController.m [462:487]:
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                completion:^(FIRAuthCredential *_Nullable credential, NSError *_Nullable error) {
              [self showSpinner:^{
                 if (error) {
                   [self hideSpinner:^{
                     [self showMessagePrompt:error.localizedDescription];
                     return;
                   }];
                 }
                if (credential) {
                  [[FIRAuth auth] signInWithCredential:credential
                                            completion:^(FIRAuthDataResult *_Nullable authResult,
                                                         NSError *_Nullable error) {
                    [self hideSpinner:^{
                      if (error) {
                        [self showMessagePrompt:error.localizedDescription];
                        return;
                      }
                    }];
                  }];
                }
              }];
            }];
            // [END firebase_auth_microsoft]
        }];
      }
      break;
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