Describe the problem

expressJwtSecret in the GetVerificationKey mode can return a Promise of undefined, e.g. here:

    if (!token) { return; }

but GetVerificationKey returns Secret | Promise<Secret> to which undefined or Promise are not assignable.

What was the expected behavior?

The typing for GetVerificationKey should include undefined.

Reproduction

This fails to compile:

const x: Awaited<ReturnType<GetVerificationKey>> = undefined;

Environment

• Version of this library used:: 2.1.4