code: func (c *Capability) AllowClientOutgoing(appSid string, appParams map[string]string) {
  	c.shouldBuildOutgoingScope = true
  	c.appSid = appSid
  	c.outgoingParams = appParams
  }
docs: // Allows this client to call your application with id `appSid` (See https://www.twilio.com/user/account/apps).
  // When the call connects, Twilio will call your voiceUrl REST endpoint.
  // The `appParams` argument will get passed through to your voiceUrl REST endpoint as GET or POST parameters.