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Revise MSI V2 token acquisition process documentation #5512

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Revise MSI V2 token acquisition process documentation #5512

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3729ed6
Revise MSI V2 token acquisition process documentation
bgavrilMS Oct 2, 2025
6b61d0c
Update msi_with_credential_design.md
bgavrilMS Oct 8, 2025
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27 changes: 25 additions & 2 deletions docs/msi_v2/msi_with_credential_design.md
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,8 @@ The primary objective is to enable seamless token acquisition in MSI V2 for VM/V

In **MSI V1**, IMDS or any other Managed Identity Resource Provider (MIRP) directly returns an **access token**. However, in **MSI V2**, the process involves few more steps:

Conceptual diagram

```mermaid
sequenceDiagram
participant App as Application
Expand All @@ -24,10 +26,31 @@ sequenceDiagram
participant MAA as Azure MAA
participant ESTS as Entra STS (mTLS)

App ->> MSAL: AcquireTokenForManagedIdentity()
App ->> MSAL: AcquireToken
MSAL -> MSAL: Detect that MSIv2 is available, otherwise bail
MSAL -> MSAL: Create the strongest key possible, e.g. in the TPM
MSAL ->> MAA: Acquire an attestation token, which proves the key strength
MSAL ->> IMDS: Certificate Signing Request with (key, attestation token)
IMDS -->> MSAL: Certificate associated with key
MSAL ->> ESTS: Open mTLS connection to ESTS with this certificate and acquire token
ESTS -->> MSAL: token with special claim xms_tb
MSAL -->> App: token and certificate
```

Technical diagram

```mermaid
sequenceDiagram
participant App as Application
participant MSAL
participant IMDS
participant MAA as Azure MAA
participant ESTS as Entra STS (mTLS)

App ->> MSAL: AcquireToken
MSAL ->> IMDS: GET /metadata/identity/getPlatformMetadata
IMDS -->> MSAL: client_id, tenant_id, cuid, maa_endpoint

alt Attestable CU
MSAL ->> MAA: POST /attest/keyguard (attestation info)
MAA -->> MSAL: attestation_token
Expand Down
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