getProviderIdFromAuthMethod(authMethod) {
    let providerId = null;
    // For each supported provider.
    this.getSignInOptions_().forEach(option => {
      // Check for matching authMethod.
      if (option['authMethod'] === authMethod) {
        // Get the providerId for that provider.
        providerId = option['provider'];
      }
    });
    // Return the corresponding provider ID.
    return providerId;
  }
Returns the corresponding Firebase Auth provider ID for the googleyolo
authMethod provided.
@param {?string} authMethod The googleyolo authMethod whose corresponding
    Firebase provider ID is to be returned.
@return {?string} The corresponding Firebase provider ID if available.