Using own domain for cognito. Rejected bc no A record. But I have one.

Question

I've got a user pool and under app integration, domain name, I'm attempting to "use your own domain". When I put my www.mydomain.com into the field, it is rejected with  
  
**Custom domain is not a valid subdomain: Was not able to resolve the root domain, please ensure an A record exists for the root domain.**  
  
My domain _ cloudfront _ the origin S3 bucket all respond to both www and non-www requests in a browser and the route53 config has an alias A record pointing to the s3 bucket.  
  
So I have an A record and it is valid. But still being rejected.  
  
Could this be because my A record is an alias and not a pointer to a true IP address? If not, what's the issue?

Answer

I was trying to use "mydomain.com" in cognito which didn't work. And I couldn't immediately use "auth.mydomain.com" because my certificate didn't include that hostname.    
  
I solved this by removing my cert from my cloudwatch distribution, deleting the cert and recreating it, this time with a new hostname "auth.mydomain.com" (in addition to the others). Once the subdomains were verified (in my case, through CNAMEs in Route53), I reattached the cert to my cloudwatch distro.  
  
Then, in the cognito interface, I was able to use my own "auth.mydomain.com" domain. (The A record for "auth.mydomain.com" is an alias, so that wasn't the issue.)

Using own domain for cognito. Rejected bc no A record. But I have one.

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