This was one of those Duh! errors, that looked like below.
Once upon a time, I was getting Sitecore ready to roll for a client on Azure. Sitecore spun everything up for us. I got the code copied over and everything started working. The first complaint the client had was those long complicated hostnames. i.e. https://mc-abcdef-1111-2222-3333-asdqwe-cm.azurewebsites.net, but that’s another blog post for another day.
I got everything working as the go-live date started approaching fast. Was time for a final clean up and set up and along came the custom domain name to map to that server. CD went fine. CM site showed up on the sm.website.com perfectly ok but alas! going to /Sitecore/login started erroring out. I freaked me out a little bit as I have not faced this error on my 4 years of setting this monster up.
First stop, I always bug those Sitecore support people. They are awesome and very responsive. They may block me soon for creating too many premature tickets but it gives me peace of mind knowing that someone else is on it other than me.
But how I fixed it?
Go to your SI server. Head on over to Azure app service editor. Find the Sitecore.IdentityServer.Host.xml file inside Config/production/ folder.
and then you know what to do from the other more useful blog posts 🙂
Add this line inside <AllowedCorsOrigins> tag:
<AllowedCorsOriginsGroup1>http://cm.website.com|https://</AllowedCorsOriginsGroup1>
see, the mistake I did was not look inside the production folder above. the file you want is inside the production folder and not the one on the root. That one is empty. My bad.
OH! You also need to restart the app pool on the SI server. I have no idea how to do that on Azure. So, I restarted the app service. things started working as expected.
~ When in doubt, as an expert, & when you solve it, write it down for someone else. ~