tl;dr: mirall doesn't use the system certificate store. Upstream has recommended that I suggest that Rawhide update to the 2.0.2 release, so that may fix this issue.

Description of problem:
I am experiencing this error message when I start the OwnCloud client, configured to connect to my server with a Let's Encrypt certificate:

Warnings about current SSL Connection:
The issuer certificate of a locally looked up certificate could not be found
with Certificate electronsweatshop.com
Organization: <not specified>
Unit: <not specified>
Country: <not specified>
Fingerprint (MD5): 02:d5:6b:f9:2c:23:b1:05:e7:e2:f9:fb:d7:e2:60:64
Fingerprint (SHA1): 09:71:46:51:df:2a:e3:99:5e:5f:6a:5d:f6:a2:4a:a7:24:05:98:de

Effective Date: Sun Nov 1 03:15:00 2015
Expiration Date: Sat Jan 30 03:15:00 2016
Issuer: Let's Encrypt Authority X1
Organization: Let's Encrypt
Unit: 
Country: US

I am confident that I have configured the httpd server correctly (using the correct key, certificate, and CA chain) as the following clients accept the certificate without issue: Firefox, Seamonkey, curl, openssl s_client, Miredo, Psi, and Conversations (Android).

There are a couple possible explanations for this issue:

0) The client cannot use certificate chains.
1) The client does not trust the DST Root CA X3, which has cross signed the Let's Encrypt certificate. This would be surprising, since DST is a widely trusted certificate authority and every other program on my computer does not have any issue with trusting it.

I don't have an easy way to diagnose these two possibilities, but I do know that the OwnCloud client has a few issues where it does not trust system certificate stores:

https://github.com/owncloud/client/issues/2964
https://github.com/owncloud/client/issues/3739

Upstream asked me to ask Fedora to update to the 2.0.2 release, which they believe will solve this issue.

Let me know if you require any more information!

Version-Release number of selected component (if applicable):
I am running version 1.8.0 on Fedora Rawhide:

% rpm -q mirall
mirall-1.8.0-3.fc23.x86_64


How reproducible:
Every time.


Steps to Reproduce:
1. Sign the OwnCloud server's certificate with a custom certificate authority (or use Let's Encyrpt. I have tried both).
2. Install the custom CA cert on the client machine.
3. Point mirall at the OwnCloud server.


Actual results:
mirall will complain that the signing authority is untrusted.


Expected results:
mirall should trust any certificate that the system certificate store trusts. I.e., if the openssl client trusts the certificate, mirall should trust it too.


Additional info:
I've filed an upstream bug on this issue. I don't see a way to associate github issues in the external bug feature here in Bugzilla, so here's the link to the upstream report:

https://github.com/owncloud/client/issues/4062