How to easily get all HTTPS addresses that an application connects to externally?

Here are a couple of command line options.

Use watch with lsof

From this answer to Monitor outgoing web requests as they’re happening, you could use lsof and watch.

To quote the answer in its entirety:

You can use lsof and watch to do this, like so:

$ watch -n1 lsof -i TCP:80,443 

Example output

dropbox    3280 saml   23u  IPv4 56015285      0t0  TCP greeneggs.qmetricstech.local:56003->snt-re3-6c.sjc.dropbox.com:http (ESTABLISHED) 
thunderbi  3306 saml   60u  IPv4 56093767      0t0  TCP greeneggs.qmetricstech.local:34788->ord08s09-in-f20.1e100.net:https (ESTABLISHED) 
mono       3322 saml   15u  IPv4 56012349      0t0  TCP greeneggs.qmetricstech.local:54018->204-62-14-135.static.6sync.net:https (ESTABLISHED) 
chrome    11068 saml  175u  IPv4 56021419      0t0  TCP greeneggs.qmetricstech.local:42182->stackoverflow.com:http (ESTABLISHED) 

I have just tried it and it is pretty useful. You could reduce the repeat time to 0.1 seconds if you use -n0.

Just lsof

From Monitoring files continuously with lsof, you could dispense with watch and use just lsof in conjunction with the repeat (-r) option. The following repeats every two seconds

$ lsof -i TCP:80,443 -r 2

but the output isn't as pretty, although the past connections are better preserved:

=======
COMMAND  PID USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
firefox 9542 user   27u  IPv4 1068219      0t0  TCP user-300V3Z-300V4Z-300V5Z:37360->192.0.78.23:https (ESTABLISHED)
firefox 9542 user   48u  IPv4 1053405      0t0  TCP user-300V3Z-300V4Z-300V5Z:45948->ec2-54-213-37-69.us-west-2.compute.amazonaws.com:https (ESTABLISHED)
=======
COMMAND  PID USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
firefox 9542 user   27u  IPv4 1068219      0t0  TCP user-300V3Z-300V4Z-300V5Z:37360->192.0.78.23:https (ESTABLISHED)
firefox 9542 user   48u  IPv4 1053405      0t0  TCP user-300V3Z-300V4Z-300V5Z:45948->ec2-54-213-37-69.us-west-2.compute.amazonaws.com:https (ESTABLISHED)
firefox 9542 user   52u  IPv4 1138942      0t0  TCP user-300V3Z-300V4Z-300V5Z:57602->kul08s01-in-f10.1e100.net:https (SYN_SENT)
firefox 9542 user  102u  IPv4 1139934      0t0  TCP user-300V3Z-300V4Z-300V5Z:49102->kul09s13-in-f14.1e100.net:https (ESTABLISHED)
firefox 9542 user  110u  IPv4 1138950      0t0  TCP user-300V3Z-300V4Z-300V5Z:49104->kul09s13-in-f14.1e100.net:https (SYN_SENT)
=======
...
=======
COMMAND  PID USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
firefox 9542 user   27u  IPv4 1068219      0t0  TCP user-300V3Z-300V4Z-300V5Z:37360->192.0.78.23:https (ESTABLISHED)
firefox 9542 user   48u  IPv4 1053405      0t0  TCP user-300V3Z-300V4Z-300V5Z:45948->ec2-54-213-37-69.us-west-2.compute.amazonaws.com:https (ESTABLISHED)
firefox 9542 user   51u  IPv4 1140129      0t0  TCP user-300V3Z-300V4Z-300V5Z:52284->kul09s13-in-f10.1e100.net:https (ESTABLISHED)
firefox 9542 user  108u  IPv4 1137384      0t0  TCP user-300V3Z-300V4Z-300V5Z:55886->103.229.10.236:https (ESTABLISHED)
firefox 9542 user  122u  IPv4 1137399      0t0  TCP user-300V3Z-300V4Z-300V5Z:55870->kul08s12-in-f1.1e100.net:https (ESTABLISHED)
firefox 9542 user  126u  IPv4 1137402      0t0  TCP user-300V3Z-300V4Z-300V5Z:47370->stackoverflow.com:https (SYN_SENT)

Note: Every two seconds interval is separated by =======.

See also how to find URLs accessed by a process, although, given the promising title, the two answers unfortunately don't seem to provide a filter on a per application, or per process, basis.

Other useful tricks with lsof are described here, 15 Linux lsof Command Examples (Identify Open Files), which would allow you to filter the results of lsof more, so that you can customise the commands above to more your taste.