feat: MFA APIs

[tusharpandey13]

Important

This PR is the 2nd PR in a PR stack
Current base: #2480

Adds MFA API support, enabling getAuthenticators, enroll, challenge and verify functionality.

Changes

• Added MfaClient classes for server and client
• Added business logic for getAuthenticators, enroll, challenge and verify
• Added server handlers for the same
• Added flow tests for client and server scenarios
• Added documentation

Tests

Added flow tests testing all MFA flows for server and client.

Usage

try {
  const { token } = await auth0.getAccessToken({ audience: 'https://api.example.com' });
} catch (error) {
  if (error instanceof MfaRequiredError) {

    // Get available authenticators
    const authenticators = await auth0.mfa.getAuthenticators({
      mfaToken: error.mfa_token
    });

    // Enrollment
    const enrollment = await auth0.mfa.enroll({
      mfaToken,
      authenticatorTypes: ["otp"]
    });

    // Initiate challenge
    const challenge = await auth0.mfa.challenge({
      mfaToken: error.mfa_token,
      challengeType: 'otp',
      authenticatorId: authenticators[0].id
    });

    // Verify code
    const tokens = await auth0.mfa.verify({
      mfaToken: error.mfa_token,
      otp: '123456'
    });
  }
}

[gyaneshgouraw-okta]

@tusharpandey13 enrolment signatures are slightly different from spa

https://github.com/auth0/auth0-spa-js/blob/main/EXAMPLES.md?plain=1#L890

For enrolment we are not accepting oobChannels: ["email"], in array notation, rather a simplified factorType which internally calculates oobChannel.

You can refer the above code snippet.