An agent calls an MCP server that reads blobs. The project's managed identity already holds Storage Blob Data Contributor on the storage account, but the tool call is rejected by the storage account. What should you correct?
- A.
Assign the role to the Foundry account's system-assigned identity instead of the project's
- B.
Recreate the project connection using key-based authentication so that the storage account key is passed through with each tool call instead of an Entra ID token obtained for the agent identity
- C.
Assign the role to the agent identity, because the managed identity only authenticates the blueprint and the agent identity is the principal the downstream resource authorises
- D.
Grant the project managed identity the Foundry User role on the storage account
Show answer
Answer: C
The agent identity, not the project managed identity, is the principal that needs RBAC on the downstream resource.
- A. Moving the assignment between Foundry identities does not help, because neither is the principal presented to the storage account.
- B. Reverting to keys abandons the identity model the agent tool authentication is built on and would be rejected by governance requiring keyless access.
- C. The agent identity is documented as the principal the downstream resource authorises; the managed identity only authenticates the blueprint.
- D. Foundry User grants access to the Foundry project and is not a data-plane role on a storage account.