Add GovSGCloud sovereign cloud environment

Co-authored-by: gavinbarron <7122716+gavinbarron@users.noreply.github.com>

Author: Copilot

src/Authentication/Authentication.Test/Common/GraphSettingsTests.cs

@@ -115,8 +115,8 @@ public void ShouldLoadSettingsFromConfiguredDataStore()
 
             // Assert
             Assert.NotNull(loadedEnvironment);
-            // 6 built-in + 2 user-defined
-            Assert.Equal(8, settings.Environments.Count());
+            // 7 built-in + 2 user-defined
+            Assert.Equal(9, settings.Environments.Count());
             Assert.Equal("https://login.MyNewCloud.com", loadedEnvironment.AzureADEndpoint);
             Assert.Equal("https://graph.MyNewCloud.com", loadedEnvironment.GraphEndpoint);
             Assert.Equal(GraphEnvironmentConstants.EnvironmentType.UserDefined, loadedEnvironment.Type);
@@ -155,8 +155,8 @@ public void ShouldRemoveSettingsFromConfiguredDataStore()
 
             // Assert
             Assert.NotEmpty(settingsContent);
-            // 6 built-in + 1 user-defined
-            Assert.Equal(7, settings.Environments.Count());
+            // 7 built-in + 1 user-defined
+            Assert.Equal(8, settings.Environments.Count());
 
             GraphSession.Reset();
         }

src/Authentication/Authentication/GraphEnvironmentConstants.cs

@@ -43,6 +43,11 @@ public static class EnvironmentName
             /// The German sovereign cloud operated by Delos.
             /// </summary>
             public const string DelosCloud = "DelosCloud";
+
+            /// <summary>
+            /// The Singapore government sovereign cloud.
+            /// </summary>
+            public const string GovSGCloud = "GovSGCloud";
         }
 
         /// <summary>
@@ -118,6 +123,16 @@ public static class EnvironmentType
                     AzureADEndpoint = "https://login.sovcloud-identity.de",
                     GraphEndpoint = "https://graph.svc.sovcloud.de"
                 }
+            },
+            // Singapore government sovereign cloud endpoints.
+            {
+                EnvironmentName.GovSGCloud, new GraphEnvironment
+                {
+                    Name = EnvironmentName.GovSGCloud,
+                    Type = EnvironmentType.BuiltIn,
+                    AzureADEndpoint = "https://login.sovcloud-identity.sg",
+                    GraphEndpoint = "https://graph.svc.sovcloud.sg"
+                }
             }
         };
     }