The first time you sign in to AYSO using single sign-on, you will see the following instructions and login screen from UCOP. Log in using your existing password (for new users that would be your birthdate, such as 01311999 for January 31, 1999). Note that if you click on "Why am I being asked for my password" you will receive the screen shown below ("password help").
In the following screen, if you want single sign-on, you should accept the first option, the single sign-on option, which allows your campus sign-on account (Hastings email account name) to go directly to AYSO without interposing the traditional AYSO login screen and password authentication:
Henceforth, you can log in to At Your Service Online by entering your Hastings campus sign-on account name (email name) and password in the sign-on page as shown below.