ClientCertificateCredential: better exception message for unsupported file extensions (#5197)

* Cert Cred: better exception message for unsupported file extensions

* fix spelling

* Make it better

* Empty path case

* adfs

---------

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

.vscode/cspell.json

@@ -52,6 +52,7 @@
     "ABFS",
     "ABNF",
     "adamdebreceni",
+    "adfs",
     "Adls",
     "ahojnnes",
     "ahsonkhan",

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

@@ -9,6 +9,7 @@
 #include <azure/core/base64.hpp>
 #include <azure/core/datetime.hpp>
 #include <azure/core/internal/cryptography/sha_hash.hpp>
+#include <azure/core/internal/strings.hpp>
 #include <azure/core/io/body_stream.hpp>
 #include <azure/core/platform.hpp>
 #include <azure/core/uuid.hpp>
@@ -399,16 +400,33 @@ ClientCertificateCredential::ClientCertificateCredential(
     CertificateThumbprint mdVec;
     try
     {
+      if (clientCertificatePath.empty())
+      {
+        throw AuthenticationException("Certificate file path is empty.");
+      }
+
+      using Azure::Core::_internal::StringExtensions;
+      std::string const PemExtension = ".pem";
+      auto const certFileExtensionStart = clientCertificatePath.find_last_of('.');
+      auto const certFileExtension = certFileExtensionStart != std::string::npos
+          ? clientCertificatePath.substr(certFileExtensionStart)
+          : std::string{};
+
+      if (!StringExtensions::LocaleInvariantCaseInsensitiveEqual(certFileExtension, PemExtension))
+      {
+        throw AuthenticationException(
+            "Certificate format"
+            + (certFileExtension.empty() ? " " : " ('" + certFileExtension + "') ")
+            + "is not supported. Please convert your certificate to '" + PemExtension + "'.");
+      }
+
       std::tie(mdVec, m_pkey) = ReadPemCertificate(clientCertificatePath);
     }
-    catch (AuthenticationException&)
-    {
-      throw;
-    }
-    catch (std::exception& e)
+    catch (std::exception const& e)
     {
       // WIL does not throw AuthenticationException.
-      throw AuthenticationException(e.what());
+      throw AuthenticationException(
+          std::string("Identity: ClientCertificateCredential: ") + e.what());
     }
 
     // Get thumbprint as hex string:

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

@@ -148,6 +148,77 @@ TEST_P(GetCredentialName, )
   EXPECT_EQ(cred.GetCredentialName(), "ClientCertificateCredential");
 }
 
+TEST(ClientCertificateCredential, UnsupportedExtension)
+{
+  try
+  {
+    ClientCertificateCredential const cred(
+        "01234567-89ab-cdef-fedc-ba8976543210", "fedcba98-7654-3210-0123-456789abcdef", "file.pfx");
+
+    EXPECT_TRUE(
+        !"ClientCertificateCredential with unsupported extension (.pfx) is supposed to throw.");
+  }
+  catch (Azure::Core::Credentials::AuthenticationException const& ex)
+  {
+    EXPECT_EQ(
+        ex.what(),
+        std::string("Identity: ClientCertificateCredential: "
+                    "Certificate format ('.pfx') is not supported. "
+                    "Please convert your certificate to '.pem'."));
+  }
+
+  try
+  {
+    ClientCertificateCredential const cred(
+        "01234567-89ab-cdef-fedc-ba8976543210",
+        "fedcba98-7654-3210-0123-456789abcdef",
+        "file.cert");
+
+    EXPECT_TRUE(
+        !"ClientCertificateCredential with unsupported extension (.cert) is supposed to throw.");
+  }
+  catch (Azure::Core::Credentials::AuthenticationException const& ex)
+  {
+    EXPECT_EQ(
+        ex.what(),
+        std::string("Identity: ClientCertificateCredential: "
+                    "Certificate format ('.cert') is not supported. "
+                    "Please convert your certificate to '.pem'."));
+  }
+
+  try
+  {
+    ClientCertificateCredential const cred(
+        "01234567-89ab-cdef-fedc-ba8976543210",
+        "fedcba98-7654-3210-0123-456789abcdef",
+        "noextension");
+
+    EXPECT_TRUE(!"ClientCertificateCredential without an extension is supposed to throw.");
+  }
+  catch (Azure::Core::Credentials::AuthenticationException const& ex)
+  {
+    EXPECT_EQ(
+        ex.what(),
+        std::string("Identity: ClientCertificateCredential: "
+                    "Certificate format is not supported. "
+                    "Please convert your certificate to '.pem'."));
+  }
+
+  try
+  {
+    ClientCertificateCredential const cred(
+        "01234567-89ab-cdef-fedc-ba8976543210", "fedcba98-7654-3210-0123-456789abcdef", "");
+
+    EXPECT_TRUE(!"ClientCertificateCredential with an empty path is supposed to throw.");
+  }
+  catch (Azure::Core::Credentials::AuthenticationException const& ex)
+  {
+    EXPECT_EQ(
+        ex.what(),
+        std::string("Identity: ClientCertificateCredential: Certificate file path is empty."));
+  }
+}
+
 TEST(ClientCertificateCredential, GetOptionsFromEnvironment)
 {
   {