Convert a dictionary to string joining each key/value for a keyValueToken and mark each group by another token

DicionaryJoinString.swift

extension Dictionary {
    
    func joinKeyValuesFor(keyValueToken : String, groupedByToken:String ) -> String
    {
        var str = ""
        
        for (key, value) in self
        {
            if str != ""
            {
                str += groupedByToken
            }
            
            str += "\(key)\(keyValueToken)\(value)"
        }
        
        return str
    }
    
}


["user":"guest", "password":"12345", "grant":"password"].joinKeyValuesFor("=", groupedByToken: "&")
//Returns : "grant=password&user=dede&password=12345"