Working example of UIActivityItemProvider customising a shared URL depending on the activity type. http://benjaminmayo.co.uk/twitter-app-sharing-link-garbage

ViewController.swift

import UIKit

class ViewController : UIViewController {
    // Monotonous view setup hidden. Imagine there's a button on screen that gets tapped and fires the action below.
    
    @IBAction func shareLinkButtonPressed(_ sender: Any) {
        let urlToShare = URL(string: "http://twitter.com/bzamayo")! // the base URL, in a real app this would be provided dynamically based on the current context 
        let sharingActivityItemProvider = LinkSharingActivityItemProvider(url: urlToShare) // make an activity item provider, defined below
        
        let activityViewController = UIActivityViewController(activityItems: [sharingActivityItemProvider], applicationActivities: nil)
        self.present(activityViewController, animated: true, completion: nil)
    }
}

public class LinkSharingActivityItemProvider : UIActivityItemProvider {
    public let sharingURL: URL
    
    public init(url: URL) {
        self.sharingURL = url
        
        super.init(placeholderItem: url)
    }
    
    public override var item: Any { // customise the item for the current `activityType`
        var components = URLComponents(url: self.sharingURL, resolvingAgainstBaseURL: true)!
        
        if let activityType = self.activityType {
            let rawActivityValue = activityType.rawValue
            let queryValue = "twcamp^share|twsrc^ios|twgr^\(rawActivityValue)"
            
            let queryItem = URLQueryItem(name: "ref_src", value: queryValue)
            
            components.queryItems = (components.queryItems ?? []) + [queryItem]
        }
        
        return components.url!
    }
}