A cloud-based identity and access management service for securing user authentication and resource access
Yes, this is possible. He can provide you with access to his Azure tenant by adding your external account as a guest user - https://learn.microsoft.com/en-us/azure/active-directory/external-identities/b2b-quickstart-add-guest-users-portal and then he can assign the required permissions to his Azure subscription - https://learn.microsoft.com/en-us/azure/role-based-access-control/role-assignments-portal?tabs=current