intercepter.ts

import { CallHandler, ExecutionContext, Injectable, NestInterceptor } from '@nestjs/common';
import { Observable, Observer } from 'rxjs';
import { flatMap } from 'rxjs/operators';

const nextAndComplete = <T>(observer: Observer<T>, value?: T): void => {
  observer.next(result);
  observer.complete();
};

@Injectable()
export class LoginInterceptor implements NestInterceptor {
  intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
    const req = context.switchToHttp().getRequest();
    return new Observable(observer =>
      req.logIn(req.user, err => err ? observer.error(err) : nextAndComplete(observer))
    )).pipe(
      flatMap(() => next.handle())
    );
  }
}