为什么我不能从 AuthResponseData 接口访问该属性？

Question

I just wrote this code, but I can't access the property of the AuthResponseData interface (in the signup-method). I'm using Firebase as my backend.

export interface AuthResponseData{
  kind:string,
  idToken:string,
  email:string,
  refreshToken:string,
  expiresIn:string,
  localId:string,
  registered?:string
}

@Injectable({
  providedIn:'root'
})
export class AuthService{

  user = new Subject<User>();

  constructor(private http: HttpClient){}

  signup(email:string, password:string){
    return this.http.post<AuthResponseData>('https://identitytoolkit.googleapis.com/v1/accounts:signUp?key=AIzaSyAurYt47nxuRQNu9qseIdmD_aL1pmpw3lU',
    {
      email: email,
      password: password,
      returnSecureToken: true
    }).pipe(catchError(this.handleError), tap(resData => {
      ** Here I want to write: 'console.log(resData.expiresIn)'**. Actually what I really want to 
         write is more complex, but I wanted to make this problem easier to understand.
    }))
  }
  }
}

Answer 1

I guess the observable returned by signup is not subscribed by anyone.

HTTP post will not be issued until it is subscribed by anyone.