Return only unique accounts from credential stores

src/shared/Core/Interop/Linux/SecretServiceCollection.cs

@@ -39,7 +39,7 @@ public SecretServiceCollection(string @namespace)
 
         public IList<string> GetAccounts(string service)
         {
-            return Enumerate(service, null).Select(x => x.Account).ToList();
+            return Enumerate(service, null).Select(x => x.Account).Distinct().ToList();
         }
 
         public ICredential Get(string service, string account)

src/shared/Core/Interop/MacOS/MacOSKeychain.cs

@@ -66,15 +66,15 @@ public IList<string> GetAccounts(string service)
                         if (typeId == CFArrayGetTypeID())
                         {
                             int len = (int)CFArrayGetCount(resultPtr);
-                            var accounts = new List<string>(len);
+                            var accounts = new HashSet<string>(len);
                             for (int i = 0; i < len; i++)
                             {
                                 IntPtr dict = CFArrayGetValueAtIndex(resultPtr, i);
                                 string account = GetStringAttribute(dict, kSecAttrAccount);
                                 accounts.Add(account);
                             }
 
-                            return accounts;
+                            return accounts.ToList();
                         }
 
                         throw new InteropException($"Unknown keychain search result type CFTypeID: {typeId}.", -1);

src/shared/Core/Interop/Windows/WindowsCredentialManager.cs

@@ -26,7 +26,7 @@ public WindowsCredentialManager(string @namespace = null)
 
         public IList<string> GetAccounts(string service)
         {
-            return Enumerate(service, null).Select(x => x.UserName).ToList();
+            return Enumerate(service, null).Select(x => x.UserName).Distinct().ToList();
         }
 
         public ICredential Get(string service, string account)

src/shared/Core/PlaintextCredentialStore.cs

@@ -25,7 +25,7 @@ public PlaintextCredentialStore(IFileSystem fileSystem, string storeRoot, string
 
         public IList<string> GetAccounts(string service)
         {
-            return Enumerate(service, null).Select(x => x.Account).ToList();
+            return Enumerate(service, null).Select(x => x.Account).Distinct().ToList();
         }
 
         public ICredential Get(string service, string account)

src/shared/TestInfrastructure/Objects/TestCredentialStore.cs

@@ -16,7 +16,7 @@ public TestCredentialStore()
 
         public IList<string> GetAccounts(string service)
         {
-            return Query(service, null).Select(x => x.Account).ToList();
+            return Query(service, null).Select(x => x.Account).Distinct().ToList();
         }
 
         ICredential ICredentialStore.Get(string service, string account)