WebView加header

写一个类继承NSURLProtocol，在 + (BOOL)canInitWithRequest:(NSURLRequest *)request 方法拦截request为request添加请求头，这样所有的webview操作请求都会调到这里，为request添加请求头，而且不影响webview的goBack方法返回

+ (void)load {
    
    [NSURLProtocol registerClass:self];
    
}

+ (BOOL)canInitWithRequest:(NSURLRequest *)request {
    
    if ([request isKindOfClass:[NSMutableURLRequest class]]) {
        
        
        [(id)request setValue:@"iOS" forHTTPHeaderField:@"Authorization"];
            
    }
    
    return NO;
    
}