发送到客户端后无法设置标题 - 谷歌登录错误

Question

I am working through an authentication application from devchallenges.io . So far, I've been able to set up the basic login with email and password. I'm now trying to set up google login auth. When testing the server with Postman I get the error Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client. The app seems to stills work as a json web token is returned so not too sure why I'm getting this error.

server.js

// @route    POST auth/google
// @desc     auth user with google
// @access   Public
app.post('/auth/google', (req, res) => {
  const { token } = req.body;
  const CLIENT_ID =
    '1068367393637-jtuoidgq5mi5krd5q31u9ncjovt3fvgh.apps.googleusercontent.com';
  const client = new OAuth2Client(CLIENT_ID);

  let { email, name, picture, password } = '';

  async function verify() {
    const ticket = await client.verifyIdToken({
      idToken: token,
      audience: CLIENT_ID,
    });
    const payload = ticket.getPayload();
    const userid = payload['sub'];

    email = payload.email;
    name = payload.name;
    picture = payload.picture;
    password = generator.generateMultiple({
      length: 6,
    });

    try {
      // See if user exists
      let user = await AuthUser.findOne({ email });
      if (user) {
        // Return jsonwebtoken
        const payload = {
          user: {
            id: user.id,
          },
        };

        jwt.sign(
          payload,
          config.get('jwtSecret'),
          { expiresIn: '5 days' },
          (err, token) => {
            if (err) throw err;
            res.json({ token });
          }
        );
      }

      user = new AuthUser({
        name,
        email,
        picture,
        password,
      });
      // Encrypt password
      const salt = await bcrypt.genSalt(10);
      user.password = await bcrypt.hash(password, salt);
      await user.save();
      // Return jsonwebtoken
      const payload = {
        user: {
          id: user.id,
        },
      };
      jwt.sign(
        payload,
        config.get('jwtSecret'),
        { expiresIn: '5 days' },
        (err, token) => {
          if (err) throw err;
          res.json({ token });
        }
      );
    } catch (error) {
      console.error(error.message);
      res.status(500).send('Server error');
    }
  }
  verify().catch(console.error);
});

Answer 1

All I had to do was add an else conditional statement.

if (user) {
        // Return jsonwebtoken
        const payload = {
          user: {
            id: user.id,
          },
        };

        jwt.sign(
          payload,
          config.get('jwtSecret'),
          { expiresIn: '5 days' },
          (err, token) => {
            if (err) throw err;
            res.json({ token });
          }
        );
      } else {
        user = new AuthUser({
          name,
          email,
          picture,
          password,
        });
        // Encrypt password
        const salt = await bcrypt.genSalt(10);
        user.password = await bcrypt.hash(password, salt);
        await user.save();
        // Return jsonwebtoken
        const payload = {
          user: {
            id: user.id,
          },
        };
        jwt.sign(
          payload,
          config.get('jwtSecret'),
          { expiresIn: '5 days' },
          (err, token) => {
            if (err) throw err;
            res.json({ token });
          }
        );
      }