diff --git a/Sources/OAuth2Client/NXOAuth2Client.m b/Sources/OAuth2Client/NXOAuth2Client.m
index dd3843e2..3aff65b4 100644
--- a/Sources/OAuth2Client/NXOAuth2Client.m
+++ b/Sources/OAuth2Client/NXOAuth2Client.m
@@ -474,6 +474,17 @@ - (void)refreshAccessTokenAndRetryConnection:(NXOAuth2Connection *)retryConnecti
                                            clientSecret, @"client_secret",
                                            accessToken.refreshToken, @"refresh_token",
                                            nil];
+
+        if (self.additionalAuthenticationParameters) {
+            [parameters addEntriesFromDictionary:self.additionalAuthenticationParameters];
+        }
+        
+        if (self.customHeaderFields) {
+            [self.customHeaderFields enumerateKeysAndObjectsUsingBlock:^(NSString *key, NSString *obj, BOOL *stop) {
+                [tokenRequest addValue:obj forHTTPHeaderField:key];
+            }];
+        }
+
         if (self.desiredScope) {
             [parameters setObject:[[self.desiredScope allObjects] componentsJoinedByString:@" "] forKey:@"scope"];
         }
diff --git a/Sources/OAuth2Client/NXOAuth2Connection.m b/Sources/OAuth2Client/NXOAuth2Connection.m
index db90e71f..2a1156cb 100644
--- a/Sources/OAuth2Client/NXOAuth2Connection.m
+++ b/Sources/OAuth2Client/NXOAuth2Connection.m
@@ -415,10 +415,14 @@ - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLRespon
             }
         }
     }
-    if (self.statusCode == 401
-        && client.accessToken.refreshToken != nil
-        && authenticateHeader
-        && [authenticateHeader rangeOfString:@"expired_token"].location != NSNotFound) {
+    
+    BOOL shouldRefresh = (self.statusCode == 401)
+    && (client.accessToken.hasExpired)
+    && (client.accessToken.refreshToken != nil)
+    && authenticateHeader
+    && [authenticateHeader rangeOfString:@"expired_token"].location != NSNotFound;
+    
+    if (shouldRefresh) {
         [self cancel];
         [client refreshAccessTokenAndRetryConnection:self];
     } else {
diff --git a/Sources/OAuth2Client/NXOAuth2Request.h b/Sources/OAuth2Client/NXOAuth2Request.h
index aa601af5..ca795827 100644
--- a/Sources/OAuth2Client/NXOAuth2Request.h
+++ b/Sources/OAuth2Client/NXOAuth2Request.h
@@ -20,6 +20,7 @@
 @interface NXOAuth2Request : NSObject {
 @private
     NSDictionary *parameters;
+    NSDictionary *customHeaderFields;
     NSURL *resource;
     NSString *requestMethod;
     NXOAuth2Account *account;
@@ -37,6 +38,14 @@
   sendProgressHandler:(NXOAuth2ConnectionSendingProgressHandler)progressHandler
       responseHandler:(NXOAuth2ConnectionResponseHandler)responseHandler;
 
++ (void)performMethod:(NSString *)method
+           onResource:(NSURL *)resource
+      usingParameters:(NSDictionary *)parameters
+         headerFields:(NSDictionary *)headerFields
+          withAccount:(NXOAuth2Account *)account
+  sendProgressHandler:(NXOAuth2ConnectionSendingProgressHandler)progressHandler
+      responseHandler:(NXOAuth2ConnectionResponseHandler)responseHandler;
+
 
 #pragma mark Lifecycle
 
@@ -52,6 +61,7 @@
 @property (nonatomic, strong, readwrite) NSString *requestMethod;
 @property (nonatomic, strong, readwrite) NSURL *resource;
 @property (nonatomic, strong, readwrite) NSDictionary *parameters;
+@property (nonatomic, strong, readwrite) NSDictionary *customHeaderFields;
 
 
 #pragma mark Signed NSURLRequest
diff --git a/Sources/OAuth2Client/NXOAuth2Request.m b/Sources/OAuth2Client/NXOAuth2Request.m
index ad8564bd..f945f2ab 100644
--- a/Sources/OAuth2Client/NXOAuth2Request.m
+++ b/Sources/OAuth2Client/NXOAuth2Request.m
@@ -37,6 +37,7 @@ @implementation NXOAuth2Request
 + (void)performMethod:(NSString *)aMethod
            onResource:(NSURL *)aResource
       usingParameters:(NSDictionary *)someParameters
+         headerFields:(NSDictionary *)headerFields
           withAccount:(NXOAuth2Account *)anAccount
   sendProgressHandler:(NXOAuth2ConnectionSendingProgressHandler)progressHandler
       responseHandler:(NXOAuth2ConnectionResponseHandler)responseHandler;
@@ -45,9 +46,24 @@ + (void)performMethod:(NSString *)aMethod
                                                                   method:aMethod
                                                               parameters:someParameters];
     request.account = anAccount;
+    request.customHeaderFields = headerFields;
     [request performRequestWithSendingProgressHandler:progressHandler responseHandler:responseHandler];
 }
 
++ (void)performMethod:(NSString *)aMethod
+           onResource:(NSURL *)aResource
+      usingParameters:(NSDictionary *)someParameters
+          withAccount:(NXOAuth2Account *)anAccount
+  sendProgressHandler:(NXOAuth2ConnectionSendingProgressHandler)progressHandler
+      responseHandler:(NXOAuth2ConnectionResponseHandler)responseHandler;
+{
+    [self performMethod:aMethod
+             onResource:aResource
+        usingParameters:someParameters
+            withAccount:anAccount
+    sendProgressHandler:progressHandler
+        responseHandler:responseHandler];
+}
 
 #pragma mark Lifecycle
 
@@ -66,6 +82,7 @@ - (instancetype)initWithResource:(NSURL *)aResource method:(NSString *)aMethod p
 #pragma mark Accessors
 
 @synthesize parameters;
+@synthesize customHeaderFields;
 @synthesize resource;
 @synthesize requestMethod;
 @synthesize account;
@@ -105,6 +122,15 @@ - (void)performRequestWithSendingProgressHandler:(NXOAuth2ConnectionSendingProgr
     
     NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:self.resource];
     [request setHTTPMethod:self.requestMethod];
+    
+    if (self.customHeaderFields) {
+        [self.customHeaderFields enumerateKeysAndObjectsUsingBlock:^(NSString *field, NSString *value, BOOL *stop) {
+            NSAssert([field isKindOfClass:NSString.class], @"Invalid Type For Field - String Expected");
+            NSAssert([value isKindOfClass:NSString.class], @"Invalid Type For Value - String Expected");
+                [request setValue:value forHTTPHeaderField:field];
+        }];
+    }
+    
     self.connection = [[NXOAuth2Connection alloc] initWithRequest:request
                                                 requestParameters:self.parameters
                                                       oauthClient:self.account.oauthClient