Provide a way to go through MFA natively rather than in universal login

[citrocitrusyolo]

Checklist

• I have looked into the Readme, Examples, and FAQ and have not found a suitable solution or answer.
• I have looked into the API documentation and have not found a suitable solution or answer.
• I have searched the issues and have not found a suitable solution or answer.
• I have searched the Auth0 Community forums and have not found a suitable solution or answer.
• I agree to the terms within the Auth0 Code of Conduct.

Describe the problem you'd like to have solved

When using universal login (authorize) if mfa is enabled it forces the user to go through the mfa 'loop' inside the browser. A product request has been to locate the mfa loop inside of the native app and keep the initial signin step in the browser

Describe the ideal solution

When mfa is required the option to return that to the native app as token endpoint does is ideal, ie

"json": {
    "error": "mfa_required",
    "error_description": "Multifactor authentication required",
    "mfa_token": '...'
},

Then we can use that to go through enrolment and/or challenge steps inside our native app, as opposed to having to complete it in browser.

Alternatives and current workarounds

Currently we are using mfa inside the browser. We investigated:

• step-up auth for api access, however it appears to also require authorize
• second application to sign in to after initial sign in, however this seemed pretty janky
• the possibility of refresh tokens elevating perms but also seems janky

reviewed https://community.auth0.com/t/how-to-implement-mfa-step-up-when-using-auth0-js-sdk-for-authentication/27722/2

Additional context

No response

[citrocitrusyolo]

I also raised a community question for this https://community.auth0.com/t/using-react-native-auth0-how-can-i-perform-mfa-outside-of-the-browser-when-it-is-required-for-authentication/135868