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I am trying to use JWT tokens in a project I am working on at the moment. I am trying to use a middleware to verify the JWT token before passing it to the next handler. However, I have a weird issue that I do not get the JWT token in the middleware, but if I pass it to the next handler I get the token. Hopefully the example below will explain it:

I have implemented a PING method and some logging to show you what happens. My setup looks like so:

this._express.use((req, res, next) => 
 console.log('AUTH');
 return jwt.verify(req.headers['x-access-token'], 'mysecret', (err, decoded) => 
 if (err) 
 console.log(`ERROR: $err`);
 return false;
 

 console.log('DECODED');
 return next();
 );
);

//Health Check
this._express.get('/ping', (req, res) => 
 console.log(`PING`);
 return res.status(200).send('pong');
);

If I execute this piece of code the output is:

node_1 | AUTH
node_1 | ERROR: JsonWebTokenError: jwt must be provided

However, if I use the next() callback in the middleware:

this._express.use((req, res, next) => 
 console.log('AUTH');
 next(); // This is the only thing that is different
 return jwt.verify(req.headers['x-access-token'], 'mysecret', (err, decoded) => 
 if (err) 
 console.log(`ERROR: $err`);
 return false;
 

 console.log('DECODED');
 return next();
 );
);

//Health Check
this._express.get('/ping', (req, res) => 
 console.log(`PING`);
 return res.status(200).send('pong');
);

The output is the following:

node_1 | AUTH
node_1 | ERROR: JsonWebTokenError: jwt must be provided
node_1 | AUTH
node_1 | PING
node_1 | DECODED

I don't have much experience with JWT tokens, and please excuse me if it is something obvious.

So I managed to find what the issue was. The problem lies with CORS. In particular, the middleware works as expected however due to CORS a preflight request is sent which does not have the JWT token which is why I got the error in the first example. I have updated the middleware to skip the preflight requests:

 if (req.headers['access-control-request-headers'] === 'x-access-token') 
 return next();
 
 [...]

I'm guessing this to be a problem of req.headers['x-access-token']. Once next() is called, the control goes to the next endpoint route. You should provide JWT as initials to the token.