App ID and password not working on Emulator Core

[ckkashyap]

This commit broke it, e915ec1#diff-c02a923b1d3cf43295b9353b9c20e2fe.

Repro

1. Run a bot with MSA ID and password
2. Run the Emulator CLI with the same ID and password
3. Run Web Chat, pointing to the Emulator Core
4. Send "hi"

Expected

It should works, the bot should response

Actual

When Emulator Core verify the signature from POST /directline/conversations/…/activities, the Emulator Core jsonwebtoken think it is wrong and return 401 back to the bot.

[ckkashyap]

There are multiple variants of Base64 encoding, list at https://en.wikipedia.org/wiki/Base64.

In the original code, base64url.toBase64(key.n) is just translating Base64Url into Base64. It is not encoding, just turning +/ into -_, and changing the padding =.

In @justinwilaby code, Buffer.from(key.n).toString('base64') is encoding a Base64 into an extra Base64.