To create a selfie token from the user data, you need an opaqe string token, which contains the encoded user properties sent in the request. Later, the selfie token can be used as a login name. In this case, the user data is included in the selfie token, that is, the user properties are taken from the token. By the use of a selfie token, you can use your own user objects during the authentication process.
Its use, however, is limited by its relatively large size (more than 100 characters), which exceeds the maximum size of the user name in several systems.