Remove a few allocations for interfaces, which are not needed (#2414)

Author: jennyf19

src/Microsoft.Identity.Web.TokenAcquisition/AspNetCore/TokenAcquisition-AspnetCore.cs

@@ -94,7 +94,7 @@ public void ReplyForbiddenWithWwwAuthenticateHeader(
                 + $"&response_type=code&redirect_uri={application.AppConfig.RedirectUri}"
                 + $"&response_mode=query&scope=offline_access%20{string.Join("%20", scopes)}";
 
-            IDictionary<string, string> parameters = new Dictionary<string, string>()
+            Dictionary<string, string> parameters = new()
                 {
                     { Constants.ConsentUrl, consentUrl },
                     { Constants.Claims, msalServiceException.Claims },

src/Microsoft.Identity.Web.TokenAcquisition/TokenAcquisition.cs

@@ -41,12 +41,12 @@ class OAuthConstants
 #endif
         protected readonly IMsalTokenCacheProvider _tokenCacheProvider;
 
-        private readonly object _applicationSyncObj = new object();
+        private readonly object _applicationSyncObj = new();
 
         /// <summary>
         ///  Please call GetOrBuildConfidentialClientApplication instead of accessing this field directly.
         /// </summary>
-        private ConcurrentDictionary<string, IConfidentialClientApplication?> _applicationsByAuthorityClientId = new ConcurrentDictionary<string, IConfidentialClientApplication?>();
+        private readonly ConcurrentDictionary<string, IConfidentialClientApplication?> _applicationsByAuthorityClientId = new ConcurrentDictionary<string, IConfidentialClientApplication?>();
         private bool _retryClientCertificate;
         protected readonly IMsalHttpClientFactory _httpClientFactory;
         protected readonly ILogger _logger;
@@ -558,8 +558,7 @@ private bool IsInvalidClientCertificateOrSignedAssertionError(MsalServiceExcepti
         internal /* for testing */ IConfidentialClientApplication GetOrBuildConfidentialClientApplication(
            MergedOptions mergedOptions)
         {
-            IConfidentialClientApplication? application;
-            if (!_applicationsByAuthorityClientId.TryGetValue(GetApplicationKey(mergedOptions), out application) || application == null)
+            if (!_applicationsByAuthorityClientId.TryGetValue(GetApplicationKey(mergedOptions), out IConfidentialClientApplication? application) || application == null)
             {
                 lock (_applicationSyncObj)
                 {

src/Microsoft.Identity.Web/AzureADB2COpenIDConnectEventHandlers.cs

@@ -14,8 +14,8 @@ internal class AzureADB2COpenIDConnectEventHandlers
     {
         private readonly ILoginErrorAccessor _errorAccessor;
 
-        private readonly IDictionary<string, string> _userFlowToIssuerAddress =
-            new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
+        private readonly Dictionary<string, string> _userFlowToIssuerAddress =
+            new(StringComparer.OrdinalIgnoreCase);
 
         public AzureADB2COpenIDConnectEventHandlers(
             string schemeName,