Assign an administrative role to push the signature through the API

To deploy this feature, you must be a solution administrator and have Global Administrator rights.

1. To be able to deploy a signature to all your users using the API, you must assign a specific role to the administrator.

2. To do so, go to the Exchange Administration Center.

2.1 Using the link: https://outlook.office365.com/ecp/
Or
2.2 By going to your admin space from the Office 365 portal, then go to the Exchange Administration Center from this space.

3. Next, go to the permission section and add or edit an administrator role group (modified)

4. Add the ApplicationImpersonation Role to this group then add members to this group.

Result: You just have to save and wait a few minutes for Microsoft to release the group.
People added to this group will have the rights to push an API signature for all of your Office 365 users.