my-in-memory.service.ts

import { InMemoryDbService } from 'angular-in-memory-web-api'
import { RequestInfo } from 'angular-in-memory-web-api/interfaces'

export class MyInMemoryService implements InMemoryDbService {

    createDb() {
      // same as before
    }

    // HTTP POST interceptor
    post(reqInfo: RequestInfo) {
        
        // if client pinged api/authentication
        //  then call authenticate (defined below)
        if (reqInfo.collectionName === 'authentication')
            return this.authenticate(reqInfo)
        
        //  otherwise default response of In-memory DB
        return undefined
    }

    // mocking authentication happens here
    // HTTP POST interceptor handler
    private authenticate(reqInfo: RequestInfo) {
    
        // return an Observable response
        return reqInfo.utils.createResponse$(() => {
            console.log('HTTP POST api/authentication override')

            const { headers, url, req } = reqInfo

            // if request username and passord are correct
            //  return response with a JSONWebToken
            const { username, password } = req['body']
            if (username === 'fred92' && password === '1234')
                return { 
                  status: 200, 
                  headers, // reqInfo (line 30)
                  url, // reqInfo (line 30)
                  body: { 
                    token: 'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c'
                  } 
                }

            //  otherwise return response with status code 401 (unauthorized)
            return { 
              status: 401, 
              headers, 
              url, 
              body: { } 
            }
        })
    }
}