Types of property ‘responseType’ are incompatible

The version of post accepting responseType:'text' is not generic, since the result type is already clear (ie string)

this.http
.post(this.loginUrl, this.user, {responseType: 'text'}) // no generic parameter
.subscribe(
    (data) => this.success(data), // data is string
    (error) => this.failure(error)
);