Adds PayPal Partner Code

[angelleye]

Adds PayPal partner code to API requests so that PayPal can associate the app with an official partner and can then begin referring merchants and developers to use this product.

[thenbrent]

@angelleye thanks the the addition. I like idea, but the PayPal_Digital_Goods_Configuration::buttonsource() should not have a default value, and it should only be added to the request if a value has been set.

i.e.

    public static function buttonsource( $value = null ) {
        return self::set_or_get( __FUNCTION__ , $value );
    }

Then:

    protected function get_api_credentials_url(){

        $api_credentials_url = 'USER=' . urlencode( PayPal_Digital_Goods_Configuration::username() )
             . '&PWD=' . urlencode( PayPal_Digital_Goods_Configuration::password() )
             . '&SIGNATURE=' . urlencode( PayPal_Digital_Goods_Configuration::signature() )
             . '&VERSION='.  urlencode( PayPal_Digital_Goods_Configuration::version() );

        $button_source = PayPal_Digital_Goods_Configuration::buttonsource();

        if ( ! empty( $button_source ) ) {
            $api_credentials_url .='&BUTTONSOURCE=' . urlencode( $button_source );
        }

        return $api_credentials_url;
    }

I'm not really interested in working with PayPal in any partnership capacity for this library, so don't want a default with my name set on it.

[angelleye]

It's really just a benefit for end users of the library, or the merchants that end up processing payments with it. For example, a transaction that gets processed with an official partner app is less likely to get caught in a fund holding situation. So then that could be a feature/benefit you could include with your other library features.

Just a thought.

[thenbrent]

a transaction that gets processed with an official partner app is less likely to get caught in a fund holding situation

Yep, but this isn't an official partner app, it's an independent library for developers to use in their apps (whether they're an official partner or not).

As I understand it, button source is also usually a benefit to the developer, because they can negotiate a commission of transactions that go through their app using their partner ID.

In my opinion, both of these provide enough justification to leave it empty unless a developer explicitly wants to set.