How to login with OTP (email) via machine to machine backend app?

I am using the embedded login version and wish to implement the passwordless (OTP via email) approach in my backend application (Node.js) for user login. My backend is set up as a machine-to-machine application in Auth0, but I am unable to find the option to toggle on the OTP grant type in the advanced settings.

I tried updating the grant types as per the instructions in this documentation. However, I keep encountering the error message:

'Invalid grant types:'

I tried also the AuthenticationClient class from the auth0 node.js library.
I instantiated the object with my domain, clientId and clientSecret. Then called the signIn method such as:

return await auth.passwordless?.signIn({
        username: email,
        otp: code,
        realm: 'email',
        audience: config.getOrThrow('AUTH0_AUDIENCE'),

However, this approach gave me the error message:

"{\"error\":\"unauthorized_client\",\"error_description\":\"Grant type '' not allowed for the client.\",\"error_uri\":\"\"}",

I have extensively reviewed the available documentation but have not found a solution to my issue, which seems like a common type of login.

Do you have any thoughts on how to resolve this?

1 Like

Any solution for this? I’m also struggling with it.