https://azure.microsoft.com/en-us/updates/secure-your-custom-domains-at-no-cost-with-app-service-managed-certificates-preview/

On the link on the top of this post, Microsoft have created a service for assign SSL to any domain you have with any website at not cost, the steps are by far more easy than using Let’s Encrypt (which is also a good option). Is in preview but worth the try.

According to the docs it will remain for 6 month, one month before expiration will renew automatically again.