AddIssuerValidator use switch ValueTask.

Author: Brent Schmaltz

src/Microsoft.IdentityModel.Tokens/Validators.cs

@@ -215,7 +215,7 @@ public static string ValidateIssuer(string issuer, SecurityToken securityToken,
         /// <remarks>An EXACT match is required.</remarks>
         internal static string ValidateIssuer(string issuer, SecurityToken securityToken, TokenValidationParameters validationParameters, BaseConfiguration configuration)
         {
-            ValueTask<string> vt = ValidateIssuerAsync(issuer, securityToken, validationParameters, configuration);
+            Task<string> vt = ValidateIssuerAsync(issuer, securityToken, validationParameters, configuration);
             return vt.IsCompletedSuccessfully ?
                 vt.Result :
                 vt.AsTask().GetAwaiter().GetResult();

src/Microsoft.IdentityModel.Validators/AadIssuerValidator/AadIssuerValidator.cs

@@ -145,7 +145,7 @@ public string Validate(
         /// <exception cref="ArgumentNullException"> if <paramref name="securityToken"/> is null.</exception>
         /// <exception cref="ArgumentNullException"> if <paramref name="validationParameters"/> is null.</exception>
         /// <exception cref="SecurityTokenInvalidIssuerException">if the issuer is invalid or if there is a network issue. </exception>
-        internal async Task<string> ValidateAsync(
+        internal async ValueTask<string> ValidateAsync(
             string issuer,
             SecurityToken securityToken,
             TokenValidationParameters validationParameters)