Pre-populate username field with value from the query string like old Sign-In Policy
You provide policies for Sign-In, Sign-Up and Sign-In or Sign-Up. The "Sign-In" policies do not allow page customization because they are using an older (pre B2C) way of doing things. However, one advantage the Sign-In policy has is that I can add &username=myUsername and it pre-populates the Username field with this value.
In our system, we already know the username before we send them to the "sign-up or sign-in" Policy screen, and we'd like to add the username to the query string so the value is already populated.
You can use the login_hint parameter for this.
That suggested solution doesn't seem to work on B2C policies for password reset