Creating entity with external dependency inside the aggregateroot?

Question

Okay, so, I'm working on an AuthService for my microservices system.

I'm putting plenty of logic around single instance of User inside of it itself, just so I can avoid repeating code, breaking SRP or anemic domain models.

.. but now I've stumbled upon a certain problem, to be precise:

I have this method inside User entity:

    public Token SignIn(string username, string password)
    {
        if (string.IsNullOrEmpty(username))
            throw new ArgumentNullException("Username cannot be null or empty");

        if (string.IsNullOrEmpty(password))
            throw new ArgumentNullException("Password cannot be null or empty");

        if (Password != password)
            throw new Exception("Password mismatch");

        return Token.Create(this, TokenType.Session, "???");
    }

The problem with this is, token value is supposed to be generated via ITokenValueProvider.

I only see 4 solutions to this problem - all but one of them would break SRP, create a leaky abstraction or break DDD.

a) Add string tokenValue to SignIn and then generate value on the service and push it deeper.

e.g.: public Token SignIn(string username, string password, string tokenValue)

b) Add ITokenValueProvider tokenizer to SignIn and then generate it inside User.SignIn

c) Add ITokenValueProvider tokenizer to public static Token.Create() and then generate it there.

d) Replace SignIn with CanSignIn and then generate token on the service - this solution is the one that would cause no antipatterns, other than being generally ugly and disallows me to store logic around signing-in inside the entity.

Any ideas :) ?