I'm currently using Firebase Functions v1.0.3 and Firebase Admin v5.12.1. It seems to be working fine with the express NodeJS library.
Issue
However, when I tried to secure the request by sending an Authorization header:
Authorization: Bearer <token>
It did not show any logs of my tokens. I couldn't see any words that matches Bearer or Authorization Bearer (whatsoever) when I used console.log(request) inside my Firebase Functions index.js file to get the token.
All I get was the following from req.headers when I use console.log:
{ 'content-length': '0',
  'accept-language': 'en-US,en;q=0.9',
  'accept-encoding': 'gzip, deflate, br',
  referer: 'http://localhost:5000/admin/',
  accept: '*/*',
  'access-control-request-headers': 'authorization,content-type',
  'user-agent': 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.181 Safari/537.36',
  origin: 'http://localhost:5000',
  'access-control-request-method': 'GET',
  connection: 'close',
  host: 'localhost:5001' 
}
Documentation Sources
I've read a documentation about Firebase Functions Samples: Authorized HTTPS Endpoint sample codes, and some of it seems outdated.
firebase.auth().currentUser.getToken()
For instance is now:
firebase.auth().currentUser.getIdToken()
Other Libaries
I've tried to install libraries such as express-authorization-bearer and express-bearer-token, and I could still not catch the idToken.
I'm wondering if this is a NodeJS issue or a Firebase Functions issue. I'm currently using NodeJS v6.11.4
Question
How do I catch the token inside Firebase Functions using Express or any method using NodeJS?
 
    