SDK-2770 Support central auth token.

[abdalmajeed-yoti]

Adds OAuth2 Bearer token authentication as an alternative to the existing RSA signed-request authentication for the IDV client.

What's New

• AuthTokenGenerator — Generates access tokens via OAuth2 client_credentials grant with PS384-signed JWT assertions.
• IDVClient — New authToken option, mutually exclusive with sdkId/pem.

Usage

const { IDVClient, AuthTokenGenerator } = require('yoti');

// Generate an access token
const generator = new AuthTokenGenerator(sdkId, pemString);
const tokenResponse = await generator.generate(['idv:sessions']);

// Create IDV client with token auth
const idvClient = new IDVClient(null, null, { authToken: tokenResponse.getAccessToken() });

// Use as usual
const session = await idvClient.createSession(sessionSpec);

Signed-request auth continues to work unchanged:

const idvClient = new IDVClient(sdkId, pemString);