Specifying HTTP referer in embedded UIWebView

Set the referer using – setValue:forHTTPHeaderField:

NSMutableURLRequest* request = ...;
[request setValue:@"https://myapp.com" forHTTPHeaderField: @"Referer"];

But note that according to the HTTP RFC you shouldn’t, because your app is not addressable using a URI:

The Referer field MUST NOT be sent if the Request-URI was obtained
from a source that does not have its own URI, such as input from the
user keyboard.

… unless you are using a custom protocol binded to your app (myapp://blah.com/blah).

You can create one and call loadRequest: manually or intercepting a normal request made by the user.

- (BOOL) webView:(UIWebView*)webView shouldStartLoadWithRequest:(NSURLRequest*)request navigationType:(UIWebViewNavigationType) navigationType 
{
    NSDictionary *headers = [request allHTTPHeaderFields];
    BOOL hasReferer = [headers objectForKey:@"Referer"]!=nil;
    if (hasReferer) {
        // .. is this my referer?
        return YES;
    } else {
        // relaunch with a modified request
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            dispatch_async(dispatch_get_main_queue(), ^{
                NSURL *url = [request URL];
                NSMutableURLRequest* request = [NSMutableURLRequest requestWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:60.0];
                [request setHTTPMethod:@"GET"];
                [request setValue:@"https://whatever.com" forHTTPHeaderField: @"Referer"];
                [self.webView loadRequest:request];
            });
        });
        return NO;
    }
}