We can find an example of this kind on the Internet:

Here are the steps that hap­pen if you want to access Trello by using your Google account:

1. User requests access: Use the Trello login web page and select Google account as a login method.
2. Redir­ec­tion to IdP: Trello redir­ects the user to the Google login page.
3. Login page served: The user is served with the Google login page.
4. Cre­den­tials entered: The user enters their Google credentials.
5. SSO Serv­er veri­fic­a­tion: Google sends authen­tic­a­tion info to the SSO Author­iz­a­tion server
6. Authen­tic­a­tion at IdP: The Author­iz­a­tion serv­er returns the auth token (SAML) if the cre­den­tials are valid.
7. Access gran­ted: Google sends the auth token to the Trello
8. Val­id­ate token: In the last step, Trello sends the token to the Google Author­iz­a­tion serv­er to val­id­ate it
9. Token val­id: If the token is val­id, Trello will allow access to the user and store the ses­sion for future interactions
10. Allow access

Source: HOW DOES SINGLE SIGN-ON (SSO) WORK? – BY DR MILAN MILANOVIĆ

The author expressed this as a graph­ic as a dia­gram above.

In the attached doc­u­ment you will find this dia­gram expressed as a com­mu­nic­a­tion dia­gram, a sequence dia­gram and a com­pon­ent diagram.

SSO Model – UML Communications Diagram

Dia­gram above SSO Mod­el – UML Com­mu­nic­a­tions Dia­gram id an UML ver­sion sim­il­ar to ori­gin­al SSO Mod­el by Mil­an Mil­an­ovic.

Com­mu­nic­a­tion Dia­grams – Com­mu­nic­a­tion Dia­grams show inter­ac­tions through an archi­tec­tur­al view where the arcs between the com­mu­nic­at­ing Life­lines are dec­or­ated with descrip­tion of the passed Mes­sages and their sequencing.

3. SSO Model – UML Sequence Diagram

Sequence Dia­grams – The most com­mon vari­ant is the Sequence Dia­gram that focuses on the Mes­sage inter­change between a num­ber of Lifelines.

4. SSO Model Architecture HLD – UML Component Diagram

The com­pon­ents that com­mu­nic­ate with each oth­er form the above architecture.