Implement Phase 3 features for DefaultAzureCredential (#6724)

* Implement Phase 3 features for DefaultAzureCredential

* Forgotten change to update header

* Clang-format

* GCC fix

* Change 'envVarName' string parameter to a boolean 'requireEnvVarValue' parameter

* Rename EnvVarName to CredentialSpecifierEnvVarName and make it constexpr auto

* requireEnvVarValue => requireCredentialSpecifierEnvVarValue

* Clang-format

* Update unit test name

* Clang-format

* Update CHANGELOG with new features and bug fixes

---------

Co-authored-by: Anton Kolesnyk <antkmsft@users.noreply.github.com>

sdk/core/azure-core/inc/azure/core/internal/environment.hpp

@@ -12,6 +12,12 @@ namespace Azure { namespace Core { namespace _internal {
     ~Environment() = delete;
 
   public:
+    static std::string GetVariable(const std::string& name) { return GetVariable(name.c_str()); }
+    static void SetVariable(const std::string& name, const std::string& value)
+    {
+      SetVariable(name.c_str(), value.c_str());
+    }
+
     static std::string GetVariable(const char* name);
     static void SetVariable(const char* name, const char* value);
   };

sdk/core/azure-core/inc/azure/core/internal/strings.hpp

@@ -38,11 +38,13 @@ namespace Azure { namespace Core { namespace _internal {
       return IsDigit(c) || (c >= 'A' && c <= 'F') || (c >= 'a' && c <= 'f');
     }
 
-    static constexpr bool IsAlphaNumeric(char c) noexcept
+    static constexpr bool IsAlpha(char c) noexcept
     {
-      return IsDigit(c) || (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z');
+      return (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z');
     }
 
+    static constexpr bool IsAlphaNumeric(char c) noexcept { return IsDigit(c) || IsAlpha(c); }
+
     static constexpr bool IsSpace(char c) noexcept { return c == ' ' || (c >= '\t' && c <= '\r'); }
 
     static constexpr bool IsPrintable(char c) noexcept { return c >= ' ' && c <= '~'; }

sdk/identity/azure-identity/CHANGELOG.md

@@ -2,8 +2,11 @@
 
 ## 1.13.1 (2025-09-11)
 
-### Bugs Fixed
+### Features Added
 
+- Added a constructor overload for `DefaultAzureCredential` with a boolean parameter to indicate whether to throw an exception if `AZURE_TOKEN_CREDENTIALS` environment variable doesn't have a value.
+
+### Bugs Fixed
 - Fixed IMDS token requests for managed identities, which were broken by an invalid URL path in 1.12.0-beta.1. (A community contribution, courtesy of _[chewi](https://github.com/chewi)_)
 
 ### Acknowledgments

sdk/identity/azure-identity/inc/azure/identity/default_azure_credential.hpp

@@ -62,6 +62,19 @@ namespace Azure { namespace Identity {
      */
     explicit DefaultAzureCredential(Core::Credentials::TokenCredentialOptions const& options);
 
+    /**
+     * @brief Constructs `%DefaultAzureCredential`.
+     *
+     * @param requireCredentialSpecifierEnvVarValue Throw an exception if `AZURE_TOKEN_CREDENTIALS`
+     * environment variable is not set.
+     *
+     * @param options Generic Token Credential Options.
+     *
+     */
+    explicit DefaultAzureCredential(
+        bool requireCredentialSpecifierEnvVarValue,
+        Core::Credentials::TokenCredentialOptions const& options = {});
+
     /**
      * @brief Destructs `%DefaultAzureCredential`.
      *

sdk/identity/azure-identity/src/default_azure_credential.cpp

@@ -26,7 +26,18 @@ using Azure::Core::_internal::StringExtensions;
 using Azure::Core::Diagnostics::Logger;
 using Azure::Identity::_detail::IdentityLog;
 
+namespace {
+constexpr auto CredentialSpecifierEnvVarName = "AZURE_TOKEN_CREDENTIALS";
+} // namespace
+
 DefaultAzureCredential::DefaultAzureCredential(
+    Core::Credentials::TokenCredentialOptions const& options)
+    : DefaultAzureCredential(false, options)
+{
+}
+
+DefaultAzureCredential::DefaultAzureCredential(
+    bool requireCredentialSpecifierEnvVarValue,
     Core::Credentials::TokenCredentialOptions const& options)
     : TokenCredential("DefaultAzureCredential")
 {
@@ -77,10 +88,16 @@ DefaultAzureCredential::DefaultAzureCredential(
             [](auto options) { return std::make_shared<AzureCliCredential>(options); }},
     };
 
-    constexpr auto envVarName = "AZURE_TOKEN_CREDENTIALS";
-    const auto envVarValue = Environment::GetVariable(envVarName);
+    const auto envVarValue = Environment::GetVariable(CredentialSpecifierEnvVarName);
     const auto trimmedEnvVarValue = StringExtensions::Trim(envVarValue);
 
+    if (requireCredentialSpecifierEnvVarValue && trimmedEnvVarValue.empty())
+    {
+      throw AuthenticationException(
+          GetCredentialName() + ": '" + CredentialSpecifierEnvVarName
+          + "' environment variable is empty.");
+    }
+
     bool specificCred = false;
     if (!trimmedEnvVarValue.empty())
     {
@@ -92,8 +109,8 @@ DefaultAzureCredential::DefaultAzureCredential(
           specificCred = true;
           IdentityLog::Write(
               IdentityLog::Level::Verbose,
-              GetCredentialName() + ": '" + envVarName + "' environment variable is set to '"
-                  + envVarValue
+              GetCredentialName() + ": '" + CredentialSpecifierEnvVarName
+                  + "' environment variable is set to '" + envVarValue
                   + "', therefore credential chain will only contain single credential: "
                   + cred.CredentialName + '.');
           credentialChain.emplace_back(cred.Create(options));
@@ -143,7 +160,8 @@ DefaultAzureCredential::DefaultAzureCredential(
         }
       }
 
-      const auto logMsg = GetCredentialName() + ": '" + envVarName + "' environment variable is "
+      const auto logMsg = GetCredentialName() + ": '" + CredentialSpecifierEnvVarName
+          + "' environment variable is "
           + (envVarValue.empty() ? "not set" : ("set to '" + envVarValue + "'"))
           + ((devCredCount > 0)
                  ? (", therefore " + devCredNames + " will " + (isProd ? "NOT " : "")
@@ -177,10 +195,13 @@ DefaultAzureCredential::DefaultAzureCredential(
         }
 
         throw AuthenticationException(
-            GetCredentialName() + ": Invalid value '" + envVarValue + "' for the '" + envVarName
+            GetCredentialName() + ": Invalid value '" + envVarValue + "' for the '"
+            + CredentialSpecifierEnvVarName
             + "' environment variable. Allowed values are 'dev', 'prod'" + allowedCredNames
-            + " (case insensitive). "
-              "It is also valid to not have the environment variable defined.");
+            + " (case insensitive)."
+            + (requireCredentialSpecifierEnvVarValue
+                   ? ""
+                   : " It is also valid to not have the environment variable defined."));
       }
     }
   }

sdk/identity/azure-identity/test/ut/default_azure_credential_test.cpp

@@ -522,3 +522,9 @@ TEST_P(LogMessagesForSpecificCredential, )
 
   Logger::SetListener(nullptr);
 }
+
+TEST(DefaultAzureCredential, RequireCredentialSpecifierEnvVarValue)
+{
+  EXPECT_THROW(
+      static_cast<void>(std::make_unique<DefaultAzureCredential>(true)), AuthenticationException);
+}