System-assigned managed identities in Azure cannot be used across multiple Azure services. They are tied to the lifecycle of a single Azure resource and are deleted when that resource is deleted. This means that each system-assigned managed identity is unique to the resource it is enabled on and cannot be shared with other resources[3][4][5].
On the other hand, user-assigned managed identities can be used across multiple Azure services. They are created as standalone resources and can be assigned to one or more Azure resources, making them suitable for scenarios where multiple resources need to share the same identity[1][3][4].
For applications that require secure connections between multiple Azure services, using user-assigned managed identities is often recommended as they provide flexibility and ease of management across different resources[5][6].
Citations:
[1] https://www.varonis.com/blog/azure-managed-identities
[2] https://learn.microsoft.com/en-us/entra/identity/managed-identities-azure-resources/managed-identities-faq
[3] https://learn.microsoft.com/en-us/entra/identity/managed-identities-azure-resources/overview
[4] https://docs.azure.cn/en-us/entra/identity/managed-identities-azure-resources/overview
[5] https://learn.microsoft.com/en-us/azure/storage/common/multiple-identity-scenarios
[6] https://learn.microsoft.com/en-us/entra/identity/managed-identities-azure-resources/managed-identity-best-practice-recommendations
[7] https://stackoverflow.com/questions/77295986/best-practive-azure-identity-for-multiple-services
[8] https://stackoverflow.com/questions/61322079/difference-between-service-principal-and-managed-identities-in-azure