Using Paypal REST C#

I would like to use Paypal authenication service

https://www.paypal-labs.com/files/PayPal_Authentication_Service.pdf

The document is however missing some information,

<form method=post action=https://api-3tpaypal.com/nvp> 
<input type=hidden name=USER value= API_username> 
<input type=hidden name=PWD value= API_password> 
<input t开发者_如何学JAVAype=hidden name=SIGNATURE value= API_signature> 
<input type=hidden name=VERSION value=version> 
<input type=hidden name=RETURNURL value=yourReturnURL> 
<input type=hidden name=CANCELURL value=yourCancelURL> 
<input type=hidden name=LOGOUTURL value=yourLogoutURL> 
<input name=SERVICENAME1 value=Name> 
<input name=SERVICEDEFREQ1 value=Required> 
<input name=SERVICENAME2 value=Email> 
<input name=SERVICEDEFREQ2 value=Required> 
<input type=submit name=METHOD value=SetAuthFlowParam> 
</form>

What VERSION? what is SERVICENAME1, SERVICEEDFREQ1? etc?

REF: https://www.x.com/community/ppx/authentication

You do not need to send raw requests from C#. Please download and use C# libraries + Code sample from here:

https://www.x.com/community/ppx/code_samples