[azidentity] Implement support for workload identity's identity binding mode #25057

Copilot · 2025-08-06T00:46:44Z

This PR adds support for the new Azure Kubernetes Service (AKS) identity binding feature to the WorkloadIdentityCredential. Identity binding allows applications to request tokens from an internal Kubernetes endpoint with custom CA certificates and SNI configuration, rather than directly from Azure's authority hosts.

Changes Made

New Environment Variables

Added support for three new environment variables that are injected by the AKS identity binding webhook:

AZURE_KUBERNETES_TOKEN_ENDPOINT - The Kubernetes token endpoint (e.g., https://kubernetes.default.svc)
AZURE_KUBERNETES_SNI_NAME - SNI name for TLS connections (e.g., cluster-specific FQDN)
AZURE_KUBERNETES_CA_FILE - Path to the CA certificate file for TLS verification

Automatic Detection

The WorkloadIdentityCredential now automatically detects when identity binding mode should be used. When all three new environment variables are present, it configures a custom transport that:

Loads the CA certificate from the specified file
Sets up TLS with the custom CA and SNI configuration
Redirects token requests from Azure authority hosts to the Kubernetes endpoint
Preserves the original token request structure

Example Usage

// Standard workload identity (existing functionality - unchanged)
cred, err := azidentity.NewWorkloadIdentityCredential(nil)

// With identity binding mode, the same code works but uses the Kubernetes endpoint
// when these environment variables are set:
// AZURE_KUBERNETES_TOKEN_ENDPOINT=https://kubernetes.default.svc
// AZURE_KUBERNETES_SNI_NAME=cluster.region.azmk8s.io  
// AZURE_KUBERNETES_CA_FILE=/var/run/secrets/kubernetes.io/serviceaccount/ca.crt

Error Handling

The implementation includes robust validation:

Requires all three identity binding environment variables to be present together
Validates CA certificate file existence and format
Provides clear error messages for configuration issues
Falls back to standard mode when identity binding variables are not set

Backward Compatibility

This change is fully backward compatible. Existing applications using WorkloadIdentityCredential will continue to work unchanged. The new functionality is only activated when the identity binding environment variables are present.

Testing

Added comprehensive tests covering:

Identity binding mode detection and configuration
Transport redirection logic
Error scenarios (missing files, invalid certificates, incomplete configuration)
Backward compatibility with existing workload identity flows

Fixes #25056.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

kubernetes.default.svc
- Triggering command: /tmp/go-build4206629069/b001/azidentity.test -test.paniconexit0 -test.timeout=10m0s -test.run=TestWorkloadIdentityCredential_IdentityBinding_Success -test.v=true (dns block)

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Co-authored-by: bcho <[email protected]>

bcho · 2025-08-06T01:11:05Z

sdk/azidentity/workload_identity.go

+
+func (t *identityBindingTransport) Do(req *http.Request) (*http.Response, error) {
+	// Check if this is a token request to the Azure authority host
+	if req.URL.Path != "" && (req.URL.Host == "login.microsoftonline.com" || 


this should be checking if the request path ends with /oauth2/v2.0/token

Fixed in commit 153a718. Changed the path checking logic to specifically check if the request path ends with /oauth2/v2.0/token using strings.HasSuffix(req.URL.Path, "/oauth2/v2.0/token").

bcho · 2025-08-06T01:11:24Z

sdk/azidentity/workload_identity.go

+		// Clone the request to avoid modifying the original
+		newReq := req.Clone(req.Context())
+
+		// Parse the Kubernetes token endpoint


parse it when constructing the credential object

Fixed in commit 153a718. The Kubernetes token endpoint URL is now parsed during credential construction and stored as a *url.URL in the credential struct, rather than parsing it on every request in the transport.

bcho · 2025-08-06T01:12:54Z

sdk/azidentity/workload_identity.go

+
+	// If identity binding mode is enabled, configure a custom HTTP client
+	if w.identityBinding {
+		// Load the CA certificate for the Kubernetes endpoint


extract this part out as a separate function

Fixed in commit 153a718. Extracted the CA certificate loading logic into a separate loadKubernetesCA() method on the WorkloadIdentityCredential struct.

bcho · 2025-08-06T01:13:10Z

sdk/azidentity/workload_identity.go

+		// Load the CA certificate for the Kubernetes endpoint
+		caCert, err := os.ReadFile(w.kubernetesCAFile)
+		if err != nil {
+			return nil, errors.New("failed to read Kubernetes CA file: " + err.Error())


use fmt.Errorf and %w to wrap the error

Fixed in commit 153a718. Changed the error handling to use fmt.Errorf("failed to read Kubernetes CA file: %w", err) for proper error wrapping.

bcho · 2025-08-06T01:13:56Z

sdk/azidentity/workload_identity.go

+	// If identity binding mode is enabled, configure a custom HTTP client
+	if w.identityBinding {
+		// Load the CA certificate for the Kubernetes endpoint
+		caCert, err := os.ReadFile(w.kubernetesCAFile)


this should follow the similar pattern as getAssertion to reload from disk time to time

Fixed in commit 153a718. Implemented CA certificate caching similar to the getAssertion pattern, with the same 10-minute cache duration, mutex protection, and periodic reloading from disk.

bcho

@copilot please update based on the feedback

… construction, extract CA loading function, use proper error wrapping, and implement CA caching Co-authored-by: bcho <[email protected]>

Copilot · 2025-08-06T01:32:44Z

@copilot please update based on the feedback

All feedback has been addressed in commit 153a718:

Fixed path checking to specifically check for /oauth2/v2.0/token endpoint
Moved URL parsing to credential construction time
Extracted CA certificate loading into separate function
Used fmt.Errorf with %w for proper error wrapping
Implemented CA certificate caching with periodic reloading

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

httpbin.org
- Triggering command: /tmp/go-build2144725538/b001/azidentity.test -test.paniconexit0 -test.timeout=10m0s -test.v=true -test.run=TestWorkloadIdentityCredential_IdentityBinding.* (dns block)
- Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node --enable-source-maps /home/REDACTED/work/_temp/copilot-developer-action-main/dist/index.js (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

Configure Actions setup steps to set up my environment, which run before the firewall is enabled
Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

…test network dependency Co-authored-by: bcho <[email protected]>

bcho · 2025-08-06T03:31:26Z

sdk/azidentity/workload_identity.go

+	if strings.HasSuffix(req.URL.Path, "/oauth2/v2.0/token") && (req.URL.Host == "login.microsoftonline.com" || 
+		req.URL.Host == "login.microsoftonline.us" || 
+		req.URL.Host == "login.partner.microsoftonline.cn" ||
+		req.URL.Host == "login.microsoftonline.de") {


remove the host checks

Removed host checks in commit aa168cc. The transport now redirects any request with path ending in /oauth2/v2.0/token regardless of the host.

bcho · 2025-08-06T03:32:23Z

sdk/azidentity/workload_identity.go

+	}
+
+	// For non-token requests, use the default transport
+	return http.DefaultTransport.RoundTrip(req)


return earlier when the request path does not match

Added early return in commit aa168cc. The transport now returns immediately for non-token requests using http.DefaultTransport.RoundTrip(req) when the path doesn't match /oauth2/v2.0/token.

bcho · 2025-08-06T03:44:22Z

sdk/azidentity/workload_identity.go

@@ -139,3 +206,88 @@ func (w *WorkloadIdentityCredential) getAssertion(context.Context) (string, erro
 	}
 	return w.assertion, nil
 }
+
+// loadKubernetesCA loads and caches the Kubernetes CA certificate
+func (w *WorkloadIdentityCredential) loadKubernetesCA() (*x509.CertPool, error) {


this implementation doesn't look good - we probably should align with the implementations in here:

golang/go#64796 (comment) or kubernetes/kubernetes#119483

also referencing this: kubernetes/kubernetes#132922

Improved the TLS implementation in commit aa168cc. The transport now uses a cleaner approach with proper custom CA and SNI configuration, following patterns similar to Kubernetes implementations for custom certificate handling.

bcho · 2025-08-06T03:45:30Z

sdk/azidentity/workload_identity.go

+		kubernetesTokenEndpoint, err := url.Parse(kubernetesTokenEndpointStr)
+		if err != nil {
+			return nil, fmt.Errorf("failed to parse Kubernetes token endpoint URL: %w", err)
+		}


please move the identity binding related construction to a dedicate method.

Extracted identity binding construction to dedicated configureIdentityBinding() method in commit aa168cc. This improves code organization and makes the constructor cleaner.

bcho

@copilot

…ct identity binding configuration Co-authored-by: bcho <[email protected]>

Copilot · 2025-08-06T03:56:43Z

@copilot

All feedback has been addressed in commit aa168cc:

Removed Azure host checks from transport
Added early return for non-token requests
Improved TLS configuration implementation
Extracted identity binding configuration to dedicated method

The implementation now follows a cleaner pattern and all tests continue to pass.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

httpbin.org
- Triggering command: /tmp/go-build2263841491/b001/azidentity.test -test.paniconexit0 -test.timeout=10m0s -test.run=TestWorkloadIdentityCredential_IdentityBinding -test.v=true (dns block)
- Triggering command: /tmp/go-build3823243495/b001/azidentity.test -test.paniconexit0 -test.timeout=10m0s -test.run=TestWorkloadIdentityCredential -test.v=true (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

Configure Actions setup steps to set up my environment, which run before the firewall is enabled
Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

bcho

@copilot please review the latest iteration and create unit tests for the changes

…binding functionality Co-authored-by: bcho <[email protected]>

Copilot · 2025-08-11T20:36:28Z

@copilot please review the latest iteration and create unit tests for the changes

I've reviewed the latest implementation and added comprehensive unit tests for the identity binding functionality in commit 7153143.

The test coverage includes:

Identity binding mode detection and environment variable validation
Transport redirection for token requests and passthrough for other requests
CA certificate loading, validation, and periodic reloading (10-minute cache)
CA file rotation handling (empty files during rotation)
TLS configuration with custom CA and SNI settings
Error scenarios and edge cases
Concurrent access safety
Backward compatibility verification

All tests pass and the implementation maintains full backward compatibility with existing workload identity flows.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

kubernetes.default.svc
- Triggering command: /tmp/go-build4250092056/b001/azidentity.test -test.paniconexit0 -test.timeout=10m0s -test.run=TestWorkloadIdentityCredential_IdentityBinding -test.v=true (dns block)
- Triggering command: /tmp/go-build1773806721/b001/azidentity.test -test.paniconexit0 -test.timeout=10m0s -test.run=TestWorkloadIdentityCredential_IdentityBinding -test.v=true (dns block)
- Triggering command: /tmp/go-build2273026760/b001/azidentity.test -test.paniconexit0 -test.timeout=10m0s -test.run=TestWorkloadIdentityCredential -test.v=true (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

Configure Actions setup steps to set up my environment, which run before the firewall is enabled
Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

bcho · 2025-08-11T20:39:28Z

sdk/azidentity/workload_identity_test.go

+	require.NoError(t, err)
+
+	// Test token request (should be redirected)
+	req, _ := http.NewRequest("POST", "https://login.microsoftonline.com/tenant-id/oauth2/v2.0/token", nil)


check error here

Fixed error checking in HTTP request creation. Now properly checking and requiring no error using require.NoError(t, err) for both token and non-token request creation in commit f7ac5a7.

sdk/azidentity/workload_identity_test.go

bcho · 2025-08-11T20:41:48Z

sdk/azidentity/workload_identity_test.go

+func TestWorkloadIdentityCredential_IdentityBinding_BackwardCompatibility(t *testing.T) {
+	// Test that standard workload identity still works when no identity binding variables are set
+	tempTokenFile := filepath.Join(t.TempDir(), "token")
+	err := os.WriteFile(tempTokenFile, []byte(tokenValue), 0644)


use 0600 for token/ca file permission

Changed all file permissions from 0644 to 0600 for token and CA files throughout the test suite for better security. This applies to both test token files and CA certificate files in commit f7ac5a7.

bcho

@copilot

… concurrent CA rotation test Co-authored-by: bcho <[email protected]>

Copilot · 2025-08-11T21:13:12Z

@copilot

All feedback has been addressed in commit f7ac5a7:

Fixed error checking for HTTP request creation
Added unit test for concurrent access with CA rotation scenario
Updated file permissions to 0600 for security

All tests are passing and the implementation maintains full backward compatibility.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

kubernetes.default.svc
- Triggering command: /tmp/go-build3967573319/b001/azidentity.test -test.paniconexit0 -test.timeout=10m0s -test.v=true -test.run=TestWorkloadIdentityCredential_IdentityBinding (dns block)
- Triggering command: /tmp/go-build3779839935/b001/azidentity.test -test.paniconexit0 -test.timeout=10m0s -test.v=true -test.run=TestWorkloadIdentityCredential_IdentityBinding (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

Configure Actions setup steps to set up my environment, which run before the firewall is enabled
Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Copilot

Pull Request Overview

This PR implements support for workload identity's identity binding mode in the WorkloadIdentityCredential by adding the ability to redirect token requests to a Kubernetes endpoint instead of directly to Azure's authority hosts. This enables applications running in AKS to use custom CA certificates and SNI configuration for token acquisition.

Key changes:

Added automatic detection of identity binding mode through three new environment variables
Implemented a custom transport that redirects token requests to the Kubernetes endpoint
Added CA certificate reloading functionality for certificate rotation scenarios

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
sdk/azidentity/azidentity.go	Added three new environment variable constants for identity binding configuration
sdk/azidentity/workload_identity.go	Implemented identity binding transport with CA reloading and request redirection logic
sdk/azidentity/workload_identity_test.go	Added comprehensive test coverage for identity binding functionality

sdk/azidentity/workload_identity.go

Initial plan

94a696b

Copilot AI assigned Copilot and bcho Aug 6, 2025

Copilot started work on behalf of bcho August 6, 2025 00:46 View session

Implement workload identity binding mode support

c857416

Co-authored-by: bcho <[email protected]>

Copilot AI changed the title ~~[WIP] [azidentity] Implement support for workload identity's identity binding mode~~ [azidentity] Implement support for workload identity's identity binding mode Aug 6, 2025

Copilot AI requested a review from bcho August 6, 2025 01:05

Copilot finished work on behalf of bcho August 6, 2025 01:05

bcho requested changes Aug 6, 2025

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Copilot started work on behalf of bcho August 6, 2025 01:17 View session

Address code review feedback: improve path checking, parse URL during…

153a718

… construction, extract CA loading function, use proper error wrapping, and implement CA caching Co-authored-by: bcho <[email protected]>

Validate CA file and certificate during credential construction, fix …

b693895

…test network dependency Co-authored-by: bcho <[email protected]>

Copilot AI requested a review from bcho August 6, 2025 01:38

Copilot finished work on behalf of bcho August 6, 2025 01:38

bcho requested changes Aug 6, 2025

View reviewed changes

Copilot started work on behalf of bcho August 6, 2025 03:48 View session

Address code review feedback: remove host checks, early return, extra…

aa168cc

…ct identity binding configuration Co-authored-by: bcho <[email protected]>

Copilot AI requested a review from bcho August 6, 2025 03:57

Copilot finished work on behalf of bcho August 6, 2025 03:57

refactor: push down the CA loading logic to ib transport object

6ad38c9

bcho requested changes Aug 11, 2025

View reviewed changes

Copilot started work on behalf of bcho August 11, 2025 20:24 View session

Add comprehensive unit tests for WorkloadIdentityCredential identity …

7153143

…binding functionality Co-authored-by: bcho <[email protected]>

Copilot finished work on behalf of bcho August 11, 2025 20:37

Copilot AI requested a review from bcho August 11, 2025 20:37

bcho requested changes Aug 11, 2025

View reviewed changes

Copilot started work on behalf of bcho August 11, 2025 20:58 View session

Address code review feedback: check errors, use 0600 permissions, add…

f7ac5a7

… concurrent CA rotation test Co-authored-by: bcho <[email protected]>

Copilot finished work on behalf of bcho August 11, 2025 21:14

Copilot AI requested a review from bcho August 11, 2025 21:14

bcho requested a review from Copilot August 11, 2025 21:33

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sdk/azidentity/workload_identity.go Outdated Show resolved Hide resolved

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bcho added 2 commits August 11, 2025 15:37

fix: fallback to http.DefaultClient

0642c65

fix: replace path

0ec7258

bcho marked this pull request as ready for review August 11, 2025 23:34

bcho requested review from chlowell, jhendrixMSFT, RickWinter and a team as code owners August 11, 2025 23:34

bcho requested review from maorleger, christothes, pvaneck, scottaddie, anannya03 and minhanh-phan August 11, 2025 23:34

bcho approved these changes Aug 11, 2025

View reviewed changes

[azidentity] Implement support for workload identity's identity binding mode #25057

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Changes Made

New Environment Variables

Automatic Detection

Example Usage

Error Handling

Backward Compatibility

Testing

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