issueTokens(user: { id: string; username: string; role: Role; }): Promise<AuthTokens>
Returns a new session token and media token for user, as sign-up
(POST /api/users), sign-in (POST /api/sessions) and a password change
(PUT /api/me/password) answer them.
user: { id: string; username: string; role: Role; }
Promise<AuthTokens>