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I am trying to use jsonwebtoken NPM package for verifying a JWT token issued by Azure Active Directory. Following is the node.js code that I have written:

 var jwt = require('jsonwebtoken');
 var token = '<valid JWT token>';
 var x5cString = '<x5cSTring>';
 var publicKey = '-----BEGIN CERTIFICATE-----n' + x5cString + 'n-----END CERTIFICATE-----';

 var verifiedToken = jwt.verify(token, publicKey) //, verifyOptions);

Please note that in the above code I use the actual x5c String from https://login.microsoftonline.com/common/discovery/keys. This works fine and I get the expected result. But, the X5C string which is the public key keeps changing. I am trying to understand how to get this public key automatically.

EDIT

I found some sample code on Jsonwebtoken NPM package web site. In this code signingKey is what I want. Following is the code.

var jwksClient = require('jwks-rsa');
var client = jwksClient(
 jwksUri: 'https://login.microsoftonline.com/common/discovery/keys'
);
function getKey(header, callback)
 client.getSigningKey(header.kid, function(err, key) 
 var signingKey = key.publicKey );


jwt.verify(token, getKey, options, function(err, decoded) 
 console.log(decoded.foo) // bar
);

In the above code, jwt.verify calls getKey that takes header and callback as parameter. I do not understand how jwt.verify function passed 'header' parameter to the getKey. Following is the header that I have retrieved. how do I pass this header to getKey in the jwt.verify?

var decoded = jwt.decode(token, complete: true);
var header = decoded.header

Okay so I have found out the solution. Following is the final code that I have.

var jwksClient = require('jwks-rsa');
var jwt = require('jsonwebtoken');

 token = 'valid JWT token';
 var decoded = jwt.decode(token, complete: true);
 var header = decoded.header

 var verifyOptions = 
 algorithms: ['RS256'],
 header: decoded.header

 ;


 var client = jwksClient(
 jwksUri: 'https://login.microsoftonline.com/common/discovery/keys'
 );
 function getKey(header, callback)
 client.getSigningKey(header.kid, function(err, key) );
 

 jwt.verify(token, getKey, verifyOptions, function(err, decoded) 
 //This will display the decoded JWT token.
 console.log(decoded) 
 );