Service_ = function(serviceName) {
  validate_({
    'Service name': serviceName
  });
  this.serviceName_ = serviceName;
  this.params_ = {};
  this.tokenFormat_ = TOKEN_FORMAT.JSON;
  this.tokenHeaders_ = null;
  this.tokenMethod_ = 'post';
  this.expirationMinutes_ = 60;
}
Creates a new OAuth2 service.
@param {string} serviceName The name of the service.
@constructor