Export credentialUnavailableError constructor

sdk/azidentity/CHANGELOG.md

@@ -14,6 +14,9 @@
 ### Other Changes
 * `AzureCLICredential` imposes its default timeout only when the `Context`
   passed to `GetToken()` has no deadline
+* Added `NewCredentialUnavailableError()`. This function constructs an error indicating
+  a credential can't authenticate and an encompassing `ChainedTokenCredential` should
+  try its next credential, if any.
 
 ## 1.3.0-beta.1 (2022-12-13)
 

sdk/azidentity/chained_token_credential.go

@@ -81,10 +81,13 @@ func (c *ChainedTokenCredential) GetToken(ctx context.Context, opts policy.Token
 		}
 	}
 
-	var err error
-	var errs []error
-	var token azcore.AccessToken
-	var successfulCredential azcore.TokenCredential
+	var (
+		err                  error
+		errs                 []error
+		successfulCredential azcore.TokenCredential
+		token                azcore.AccessToken
+		unavailableErr       *credentialUnavailableError
+	)
 	for _, cred := range c.sources {
 		token, err = cred.GetToken(ctx, opts)
 		if err == nil {
@@ -93,12 +96,14 @@ func (c *ChainedTokenCredential) GetToken(ctx context.Context, opts policy.Token
 			break
 		}
 		errs = append(errs, err)
-		if _, ok := err.(*credentialUnavailableError); !ok {
+		// continue to the next source iff this one returned credentialUnavailableError
+		if !errors.As(err, &unavailableErr) {
 			break
 		}
 	}
 	if c.iterating {
 		c.cond.L.Lock()
+		// this is nil when all credentials returned an error
 		c.successfulCredential = successfulCredential
 		c.iterating = false
 		c.cond.L.Unlock()
@@ -108,7 +113,7 @@ func (c *ChainedTokenCredential) GetToken(ctx context.Context, opts policy.Token
 	if err != nil {
 		// return credentialUnavailableError iff all sources did so; return AuthenticationFailedError otherwise
 		msg := createChainedErrorMessage(errs)
-		if _, ok := err.(*credentialUnavailableError); ok {
+		if errors.As(err, &unavailableErr) {
 			err = newCredentialUnavailableError(c.name, msg)
 		} else {
 			res := getResponseFromError(err)

sdk/azidentity/chained_token_credential_test.go

@@ -82,11 +82,14 @@ func TestChainedTokenCredential_NilSource(t *testing.T) {
 }
 
 func TestChainedTokenCredential_GetTokenSuccess(t *testing.T) {
+	// ChainedTokenCredential should continue iterating when a source returns credentialUnavailableError, wrapped or not
 	c1 := NewFakeCredential()
 	c1.SetResponse(azcore.AccessToken{}, newCredentialUnavailableError("test", "something went wrong"))
 	c2 := NewFakeCredential()
-	c2.SetResponse(azcore.AccessToken{Token: tokenValue, ExpiresOn: time.Now().Add(time.Hour)}, nil)
-	cred, err := NewChainedTokenCredential([]azcore.TokenCredential{c1, c2}, nil)
+	c2.SetResponse(azcore.AccessToken{}, fmt.Errorf("%w", newCredentialUnavailableError("...", "...")))
+	c3 := NewFakeCredential()
+	c3.SetResponse(azcore.AccessToken{Token: tokenValue, ExpiresOn: time.Now().Add(time.Hour)}, nil)
+	cred, err := NewChainedTokenCredential([]azcore.TokenCredential{c1, c2, c3}, nil)
 	if err != nil {
 		t.Fatal(err)
 	}

sdk/azidentity/errors.go

@@ -101,24 +101,31 @@ func (*AuthenticationFailedError) NonRetriable() {
 
 var _ errorinfo.NonRetriable = (*AuthenticationFailedError)(nil)
 
-// credentialUnavailableError indicates a credential can't attempt
-// authentication because it lacks required data or state.
+// credentialUnavailableError indicates a credential can't attempt authentication because it lacks required
+// data or state
 type credentialUnavailableError struct {
-	credType string
-	message  string
+	message string
 }
 
+// newCredentialUnavailableError is an internal helper that ensures consistent error message formatting
 func newCredentialUnavailableError(credType, message string) error {
-	return &credentialUnavailableError{credType: credType, message: message}
+	msg := fmt.Sprintf("%s: %s", credType, message)
+	return &credentialUnavailableError{msg}
 }
 
-func (e *credentialUnavailableError) Error() string {
-	return e.credType + ": " + e.message
+// NewCredentialUnavailableError constructs an error indicating a credential can't attempt authentication
+// because it lacks required data or state. When [ChainedTokenCredential] receives this error it will try
+// its next credential, if any.
+func NewCredentialUnavailableError(message string) error {
+	return &credentialUnavailableError{message}
 }
 
-// NonRetriable indicates that this error should not be retried.
-func (e *credentialUnavailableError) NonRetriable() {
-	// marker method
+// Error implements the error interface. Note that the message contents are not contractual and can change over time.
+func (e *credentialUnavailableError) Error() string {
+	return e.message
 }
 
+// NonRetriable is a marker method indicating this error should not be retried. It has no implementation.
+func (e *credentialUnavailableError) NonRetriable() {}
+
 var _ errorinfo.NonRetriable = (*credentialUnavailableError)(nil)