Middleware with general request validation

[tarekziade]

We want a function to check the request for:

• status code 400, errno 106: request body was not valid json
• status code 411, errno 112: content-length header was not provided
• status code 413, errno 113: request body too large

The first one is currently handled by bodyParser - but it does not have the desired behavior

refs #53

[tarekziade]

@ckarlof is there any reusable code in FxA for this ?

[tarekziade]

After investigation (thanks @zaach!) FxA uses hapi and has this : https://github.com/mozilla/fxa-auth-server/blob/master/error.js#L190

we use express. we'll drop express.json() and create our own function to do all those checks

[tarekziade]

see #76