URLConnection.h

#import <Foundation/Foundation.h>

@interface URLConnection : NSObject <NSURLConnectionDataDelegate, NSURLConnectionDelegate>

+ (NSData *)sendSynchronousRequest:(NSURLRequest *)request
                 returningResponse:(NSURLResponse **)response
                             error:(NSError **)error;

@end

URLConnection.m

#import "URLConnection.h"

@interface URLConnection ()
@property (nonatomic, strong) NSURLConnection *connection;
@property (nonatomic, strong) NSURLCredential *credential;
@property (nonatomic, strong) NSURLResponse *response;
@property (atomic, strong) NSMutableData *responseData;
@property (nonatomic, strong) NSCondition *condition;
@property (nonatomic, strong) NSError *error;
@property (nonatomic) BOOL connectionDidFinishLoading;
@end

@implementation URLConnection

+ (NSData *)sendSynchronousRequest:(NSURLRequest *)request returningResponse:(NSURLResponse **)response error:(NSError **)error credential:(NSURLCredential *)credential {
	return [[[URLConnection alloc] init] sendSynchronousRequest:request returningResponse:response error:error credential:credential];
}

- (id)init {
	self = [super init];
	if (self) {
		self.condition = [[NSCondition alloc] init];
		self.connection = nil;
		self.connectionDidFinishLoading = NO;
		self.error = nil;
		self.response = nil;
		self.responseData = [[NSMutableData alloc] init];
		self.credential = nil;
	}
	return self;
}

- (NSData *)sendSynchronousRequest:(NSURLRequest *)request returningResponse:(NSURLResponse **)response error:(NSError **)error credential:(NSURLCredential *)credential {
	NSParameterAssert(request);
	NSAssert(!self.connection, @"This method may only be called once");
	self.credential = credential;
	self.connection = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:NO];
	[self.connection setDelegateQueue:[[NSOperationQueue alloc] init]];
	[self.connection start];
	[self waitForConnectionToFinishLoading];
	if (self.error != nil) {
		if (response) *response = nil;
		if (error) *error = self.error;
		return nil;
	}
	else {
		if (response) *response = self.response;
		if (error) *error = nil;
		return self.responseData;
	}
}

- (void)waitForConnectionToFinishLoading {
	[self.condition lock];
	while (!self.connectionDidFinishLoading) {
		[self.condition wait];
	}
	[self.condition unlock];
}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
	self.response = response;
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
	[self.responseData appendData:data];
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
	[self.condition lock];
	self.error = error;
	self.connectionDidFinishLoading = YES;
	[self.condition signal];
	[self.condition unlock];
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
	[self.condition lock];
	self.connectionDidFinishLoading = YES;
	[self.condition signal];
	[self.condition unlock];
}

- (void)connection:(NSURLConnection *)connection willSendRequestForAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge {
                 [[challenge sender] useCredential:self.credential forAuthenticationChallenge:challenge];
}

@end