Logout from an ALB session that is authenticated by Cognito

Question

Hello!  
I'm failing with logging out from a Cognito authenticated ALB session. The authentication itself works perfectly.  
I want to logout the user from the session and understand I have to delete/expire the cookie (AWSELBAuthSessionCookie-0,...) and redirect to the /logout endpoint. I also understand that the auth session cookie is HttpOnly and must be deleted server-side.  
The authenticated application is hosted on a subdomain "a.example.com". My various server-side cookie deletion attempts failed. I had for example the following response header set:

```
"set-cookie: AWSELBAuthSessionCookie-0=;Domain=a.example.com;Path=/;Max-Age=0;Secure"
```

But none of my set-cookie headers did actually delete the auth session cookie.  
Any ideas how the cookie can be deleted/expired?  
Cheers Fabian

Answer

What did the trick is omitting the domain (although in my case the authentication was setup for a hostname with a subdomain).  
This worked for me:

```
Set-Cookie "AWSELBAuthSessionCookie-0=deleted;path=/;expires=Thu, 01 Jan 1970 00:00:00 GMT;"
```

Logout from an ALB session that is authenticated by Cognito

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