Filr App with iOS 13 login fails: Unable to connect to the Filr server

With iOS 13 and later, attempts to log into the Filr server fails with the following message:

Filr
Unable to connect to the Filr server.
Contact your Filr administrator for help.
OK

Note: Prior to that failure, you may see this:

Filr
The site's security certificate is not trusted.
Do you want to continue?
Yes | No

Choosing Yes will take you to the next prompt which is the Unable to connect to the Filr server message.

Install a 3rd party certificate to the Filr server.

Workaround:
Log in with the IP address of the Filr server instead of the DNS name.

Apple changed their iOS security model with iOS 13.  See this document to learn the details of those changes.

Possibly the most relevant change listed in that document is:

TLS server certificates must present the DNS name of the server in the Subject Alternative Name extension of the certificate. DNS names in the CommonName of a certificate are no longer trusted.

Therefore, a self-signed certificate applied to the Filr server will not work with iOS 13.