New controls are being deployed to let administrators define the authorized interaction between Microsoft Teams and applications.
It will give administrators the ability to allow application and define which one(s) will be authorized for use with Teams
To manage it go to your Office 365 Administration portal and reach the Settings\Services & add-ins section
Select Microsoft Teams to access the properties and open the Apps section; you will note the display name may not be really clear sometime – hopefully this will be sorted soon
Administrators will also have the option to enable (or not) new application by default