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Backend authentication and authorization overview (preview)

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The Fabric developer workload sample has the following authentication flows on the backend side.

Authentication and authorization of requests from Fabric to the workload

Authorization header structure

The authorization header uses a specific token format:

SubjectAndAppToken1.0 subjectToken="delegated token", appToken="S2S token"

This format includes two distinct tokens:

  • subjectToken: This is a delegated token representing the user on whose behalf the operation is being performed.
  • appToken: This is a token specific to the Fabric application.

The rationale behind using a dual-token header is threefold:

  • Validation: The workload can verify that the request originated from Fabric by validating the appToken.

  • User Context: The subjectToken provides a user context for the action being performed.

  • Inter-Service Communication: The workload can acquire an On-Behalf-Of (OBO) token using the subjectToken, allowing it to call other services with a user token.

Authentication

The main authentication checks performed for the SubjectAndAppToken are:

  • Validation and parsing of the authorization header value: This is done in the FetchSubjectAndAppTokenTokenFromHeader method. The token must start with the "SubjectAndAppToken1.0" prefix and include two tokens - subjectToken and appToken.

  • Entra token properties validation: Both subjectToken and appToken are validated for common Microsoft Entra token properties in the ValidateAadTokenCommon method. These properties include token signature, token lifetime, token audience (workload app audience), and token version (1.0) and issuer.

  • appToken properties validation: The appToken shouldn't have an scp claim but should have an idtyp claim with app as the value. We also check that tid claim in the workload publisher tenant ID.

    Sample appToken claims:

    {
"aud": "api://localdevinstance/12345678-77f3-4fcc-bdaa-487b920cb7ee/Fabric.WorkloadSample/123",
"iss": "https://sts.windows.net/12345678-77f3-4fcc-bdaa-487b920cb7ee/",
"iat": 1700047232,
"nbf": 1700047232,
"exp": 1700133932,
"aio": "E2VgYLjBuv2l+c6cmm/iP/bnL2v+AQA=",
"appid": "00000009-0000-0000-c000-000000000000",
"appidacr": "2",
"idp": "https://sts.windows.net/12345678-77f3-4fcc-bdaa-487b920cb7ee/",
"idtyp": "app",
"oid": "87654321-727a-403d-b7d4-8e4a48865158",
"rh": "0.ACgAGX-u-vN3zE-9qkh7kgy37hQbaU7-v2xFr59O_foS7VLZAAA.",
"sub": "87654321-727a-403d-b7d4-8e4a48865158",
"tid": "12345678-77f3-4fcc-bdaa-487b920cb7ee",
"uti": "5bgMXs3uMUSAHCruRjACAA",
"ver": "1.0"
}

  • subjectToken properties validation: Ensure that the subjectToken includes an scp claim with the FabricWorkloadControl scope, that there's no idtyp claim present in the token, and that it has same appid as in the appToken.

    Sample subjectToken claims:

    {
"aud": "api://localdevinstance/12345678-77f3-4fcc-bdaa-487b920cb7ee/Fabric.WorkloadSample/123",
"iss": "https://sts.windows.net/12345678-77f3-4fcc-bdaa-487b920cb7ee/",
"iat": 1700050446,
"nbf": 1700050446,
"exp": 1700054558,
"acr": "1",
"aio": "ATQAy/8VAAAAUgWRMRnBo4VGHvrKRykUXOXBNKS1cHnBxLrYkZJJGSjAVyJGBecbLdSud1GUakER",
"amr": [
    "pwd"
],
"appid": "00000009-0000-0000-c000-000000000000",
"appidacr": "2",
"ipaddr": "46.117.19.50",
"name": "john doe",
"oid": "abacabac-f91e-41db-b997-699f17146275",
"rh": "0.ASgAGX-u-vN3zE-9qkh7kgy37hQbaU7-v2xFr59O_foS7VLZANQ.",
"scp": "FabricWorkloadControl",
"sub": "X0Wl85UA-uOmdkQz5MoT-hEgYZXDq9FYdS8g2bFUaZA",
"tid": "12345678-77f3-4fcc-bdaa-487b920cb7ee",
"unique_name": "user1@constso.com",
"upn": "user1@constso.com",
"uti": "_llZwmJoSUiHv-kw6tfDAA",
"ver": "1.0"
}

See IAuthenticationService.

Note

All the validations in our sample code are for version 1.0 tokens.

Authorization

Once it's been confirmed that the request originates from the Fabric service (via the appToken), it's understood that Fabric has already verified that the user has the necessary permissions to perform the action, based on Fabric's permissions metadata.

Authentication and authorization of requests from workload to Fabric

Workload control requests

Workload control APIs are special Fabric APIs that support workloads with their Fabric item lifecycle management. These APIs use the same SubjectAndAppToken1.0 authorization header format.

SubjectAndAppToken1.0 subjectToken="delegated token", appToken="S2S token"

When coming from the workload, the included tokens are:

  • subjectToken: This is a user-delegated token (obtained through the OBO flow) representing the user on whose behalf the operation is being performed. Fabric verifies that the user has the required permissions to perform the needed action.

  • appToken: This is a token specific to the workload application. Fabric checks that this is token is from the Entra app of the workload that the relevant Fabric item belongs to and that is on the workload publisher's tenant.

See the ValidatePermissions method in AuthorizationHandler.

Public APIs

For calling public Fabric APIs, the workload should acquire a standard Microsoft Entra OBO token with the relevant API scopes and pass it as a bearer token in the request's authorization header.

See FabricExtensionController.

Authentication and authorization of requests from workload FE to workload BE

Authorization header

The authorization header in a request sent from the workload FE to the workload BE uses a standard bearer token.

Authentication

The ValidateDelegatedAADToken method in the workload BE is responsible for validating the token. The primary checks performed are:

  • Token lifetime: Ensures the token is within its valid usage period.

  • Signature: Verifies the authenticity of the token.

  • Audience: Checks that the token's audience matches the workload Entra app.

  • Issuer: Validates the issuer of the token.

  • Allowed scopes: Validates the scopes that the token is permitted to access.

Authorization

Authorization is achieved by invoking the ValidatePermissions method. This method calls the resolvePermissions API in the Fabric workload-control endpoint for the relevant Fabric item and verifies that the user has the necessary permissions for the operation.