ADFS authentication return HTTP 503 error

Although this post is old, people will still come across it so to that end, for anyone who will run across this issue, try the following.

HTTP Error 503. The Service is unavailable

Cause #1: Invalid base address entered in the SAML login redirection page field.

Solution #1: Make sure your base addresses match your application and ADFS. For example, if ADFS was assigned https://sso.contosso.com/ your application should reflect the same address, https://sso.contosso.com/.

Cause #2: The ADFS services are not running.

Solution #2: Check your service account has up-to-date credentials and start or restart your ADFS services.

Cause #3: Not pointing to the correct resource endpoint, specifically, /ls.

Solution#3: Make sure your sign-on service URL is pointing to the correct resources, /adfs/ls.

https://contosso.com/adfs/ls