Explanation
Add commands to a custom group
1. In the Customize the Ribbon window under the Customize the Ribbon list, click the custom group that you want to add a command to.
2. In the Choose commands from list, click the list you want to add commands from, for example, Popular Commands or All Commands.
Graphical user interface, text, application Description automatically generated

3. Click a command in the list that you choose.
4. Click Add.
5. To see and save your changes, click OK.
Reference:
https://support.office.com/en-us/article/customize-the-ribbon-in-office-00f24ca7-6021-48d3-9514-a31a460ecb31

Reference:
https://docs.microsoft.com/en-us/azure/active-directory/develop/msal-overview

Messaging extensions allow users to interact with your web service through buttons and forms in the Microsoft Teams client. They can search, or initiate actions, in an external system from the compose message area, the command box, or directly from a message. You can then send the results of that interaction back to the Microsoft Teams client, typically in the form of a richly formatted card.