Apple Wallet (formerly Passbook) - Best way to add links
Since iOS7 you can add hyperlinks to the back of a pass and format the text that is displayed.

Simply add an &lt;a&gt; tag to the content of a field and the Apple Wallet app will render it as a clickable link. 

For example: &lt;a href="http://www.developer.apple.com"&gt;Click here&lt;/a&gt;

If you do not use an &lt;a&gt; tag but include a valid URL the Apple Wallet app will display it as clickable address.