How do I get a key for jsonwebtoken secret?

I am using the jsonwebtoken module for Node. How can I get a secret key for the jwt.sign function: jwt.sign(payload, secretOrPrivateKey, [options, callback])

According to the documentation:

secretOrPrivateKey is a string, buffer, or object containing either the secret for HMAC algorithms or the PEM encoded private key for RSA and ECDSA. In case of a private key with passphrase an object { key, passphrase } can be used (based on crypto documentation), in this case be sure you pass the algorithm option.

The key used in the example was 'shhhh', but that probably isn't secure: var jwt = require('jsonwebtoken'); var token = jwt.sign({ foo: 'bar' }, 'shhhhh');

How can I get/generate a better secret key?

To create "secure" random passwords I like to use: openssl rand -base64 60 on Linux.