add options to set basic auth header style

Author: leastprivilege

src/IdentityModel.AspNetCore.OAuth2Introspection/OAuth2IntrospectionOptions.cs

@@ -54,6 +54,14 @@ public class OAuth2IntrospectionOptions : AuthenticationSchemeOptions
         /// </summary>
         public DiscoveryPolicy DiscoveryPolicy { get; set; } = new DiscoveryPolicy();
 
+        /// <summary>
+        /// Gets or sets the basic authentication header style (RFC6749 vs RFC2617). Defaults to RFC6749.
+        /// </summary>
+        /// <value>
+        /// The basic authentication header style.
+        /// </value>
+        public BasicAuthenticationHeaderStyle BasicAuthenticationHeaderStyle { get; set; } = BasicAuthenticationHeaderStyle.Rfc6749;
+
         /// <summary>
         /// Specifies the timout for contacting the discovery endpoint
         /// </summary>

src/IdentityModel.AspNetCore.OAuth2Introspection/PostConfigureOAuth2IntrospectionOptions.cs

@@ -89,6 +89,7 @@ private async Task<IntrospectionClient> InitializeIntrospectionClient(OAuth2Intr
             {
                 client = new IntrospectionClient(
                     endpoint,
+                    headerStyle: Options.BasicAuthenticationHeaderStyle,
                     innerHttpMessageHandler: Options.IntrospectionHttpHandler);
             }
             else