How to get the user agent on iOS?

You don’t actually need to make the request in order to get the user-agent. Just return NO from the following delegate method and retain the user-Agent header:

-(BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType

It might look something like this:

-(BOOL)webView:(UIWebView *)webView
 shouldStartLoadWithRequest:(NSURLRequest *)request
 navigationType:(UIWebViewNavigationType)navigationType
{  
     userAgent = [[request valueForHTTPHeaderField:@"User-Agent"] copy]; 
     NSLog(@"user-agent: %@", userAgent);

     _webView.delegate = nil; 
     [_webView release]; 

     return NO; 
}

Mobile application in every request must send his User-Agent header with build version and device information

User agent configuration info

So, user agent should be like:

User-Agent: <AppName>/version (<system-information>) <platform> (<platform-details>) <extensions>

For iOS:

User-Agent: <AppName/<version> (<iDevice platform>; <Apple model identifier>; iOS/<OS version>) CFNetwork/<version> Darwin/<version>

How to get each of the components?

1. Headers Key - u can hardcode or use some constant values

2. AppName and version - grab from Info.plist

    let infoPlist = try? PListFile<InfoPlist>()
    let appName = infoPlist.data.bundleName
    let version = infoPlist.data.versionNumber
    let build = infoPlist.data.buildNumber
   

3. Info about Device

modelName - you can obtain like described here

    let modelName = UIDevice.current.modelName

other components:

    let platform = UIDevice.current.systemName
    let operationSystemVersion = ProcessInfo.processInfo.operatingSystemVersionString

4. CFNetwork version

    static var cfNetworkVersion: String? {
      guard
        let bundle = Bundle(identifier: "com.apple.CFNetwork"),
         let versionAny = bundle.infoDictionary?[kCFBundleVersionKey as String],
         let version = versionAny as? String
          else { return nil }
      return version
    }
   

from here

5. Darwin Version

     var systemInfo = utsname()
     uname(&systemInfo)
     let machineMirror = Mirror(reflecting: systemInfo.release)
     let darvinVersionString = machineMirror.children.reduce("") { identifier, element in
       guard let value = element.value as? Int8,
         value != 0 else {
           return identifier
       }
   
       return identifier + String(UnicodeScalar(UInt8(value)))
     }
   

from here

Result:

MyApp/1.8.199 (iOS; iPhone XS; Version 13.3 (Build 17C45)) CFNetwork/1121.2.1 Darvin/19.3.0

A simpler way to ascertain the user agent in iOS is to get it directly from a UIWebView using the accepted answer to this SO post. To quote that answer:

The solution was to create a UIWebView and then just use javascript to pull out the user agent.

UIWebView* webView = [[UIWebView alloc] initWithFrame:CGRectZero];
NSString* secretAgent = [webView stringByEvaluatingJavaScriptFromString:@"navigator.userAgent"];