message: refactor: fix typing for instance_url
diff: @@ -908,7 +908,7 @@ export class AuthInfo extends AsyncCreatable<AuthInfoOptions> {
  const oauth2 = new AuthCodeOAuth2(options);
  // Exchange the auth code for an access token and refresh token.
  - let _authFields;
  + let _authFields: TokenResponse;
  try {
  this.logger.info(
  `Exchanging auth code for access token using loginUrl: ${
  @@ -932,10 +932,8 @@ export class AuthInfo extends AsyncCreatable<AuthInfoOptions> {
  // but we don't want to create circular dependencies or lots of snowflakes
  // within this file to support it.
  const apiVersion = 'v42.0'; // hardcoding to v42.0 just for this call is okay.
  - // @ts-ignore TODO: need better typings
  - const url = `${
  - _authFields.instance_url
  - }/services/data/${apiVersion}/sobjects/User/${userId}`;
  + const instance = ensure(getString(_authFields, 'instance_url'));
  + const url = `${instance}/services/data/${apiVersion}/sobjects/User/${userId}`;
  const headers = Object.assign(
  { Authorization: `Bearer ${_authFields.access_token}` },
  SFDX_HTTP_HEADERS
  