According to MSDN documentation, to send more than 500 push notifications per day, your service needs a certificate to establish an SSL tunnel to the WNS.
I see here http://msdn.microsoft.com/library/windows/apps/ff941099(v=vs.105).aspx how to upload the certificate, but how do I get the certificate? Do I need to install the certificate the my web server hosting my services? What if I am hosting my services in Windows Azure?
Firstly, this question is about MPNS (Microsoft Push Notification Service), not WNS (Windows Notification Service). They are two separate services, with WNS being now Microsoft's preferred platform.
Microsoft provides a list of MPNS-approved CA's (certificate authorities) here:
The process for acquiring the certificate is roughly the same with all CA's. You need to create a CSR (certificate signing request) with your domain name as the certificate CN (common name), and send it to the CA. The CA charges a sum for certain validity period (typically 1, 2, or 3 years). Before the SSL certificate is issued, they normally do certain checks to ensure that you really own the domain name, e.g. by mailing the WHOIS owner of the domain and/or asking you to create a special DNS record.
Once you have your certificate, you need to install it as a client certificate in the server that makes the push notification calls to the MPNS servers. How do you do that, depends on your server architecture (.NET, Java, etc.).
you need a registered domain name and then you can register to buy a certificate, I think the cheapest I found for my app a few years ago was something like $99 but this may well be incorrect now.
Good Luck,
