I'm not sure about GCP, but Azure does offer role-based access[1] which gives you similar resource authentication magic to what IAM provides. The definition formats[2] even look fairly close to their IAM equivalents.

It's used in combination with Azure Active Directory, so the modality isn't 1:1 with AWS. But Managed Identities[3] is a feature that's rolling out across Azure which simplifies the model a bit, since it negates the need to create service principles in AAD beforehand.

[1] https://docs.microsoft.com/en-us/azure/role-based-access-con...

[2] https://docs.microsoft.com/en-us/azure/role-based-access-con...

[3] https://docs.microsoft.com/en-us/azure/active-directory/mana...