My nextcloud website is run under https://my.nextcloud.com -- not https://my.nextcloud.com/nextcloud
Document Root is /var/www/nextcloud.

Last week I solved HTTPS, SSL stuff between openproject server and nextcloud.
So I can curl between them without SSL problem now.

But when I tried to connect openproject to nextcloud, there was an error as below image.

So I followed this troubleshooting guide, (https://www.openproject.org/docs/system-admin-guide/integrations/nextcloud/#troubleshooting)

the first step was successful.

curl --location --request GET 'https://my.nextcloud.com/index.php/apps/integration_openproject/check-config' --header 'Authorization: foo'

But when I tried the second step, I cannot get the result.

curl -H 'OCS-APIRequest:true' -H 'Accept:application/json' https://my.nextcloud.com/nextcloud/ocs/v2.php/cloud/capabilities

I noticed that the URL in above command is include /nextcloud/ in path,
which is not available in my nextcloud site. (My site root is at /var/www/nextcloud)

So I tried this instead. (remove /nextcloud/ path)

curl -H 'OCS-APIRequest:true' -H 'Accept:application/json' https://my.nextcloud.com/ocs/v2.php/cloud/capabilities

Then Nextcloud site return data as it should.

My questions are ..
1. Is the 'File Storage' tried to connect 'Nextcloud' site,  by include /nextcloud/ in Requested URL?
2. If (1) was true, how do I remove that /nextcloud/ from requested URL, without re-build nextcloud site ?

Thanks !

Found the root of problem by ....

- Enable debug level log using this guide >> https://community.openproject.org/topics/9247

- view log by command

journalctl -e -o short-full SYSLOG_IDENTIFIER=openproject-web-1.service --output-fields=MESSAGE > ./op-log.txt

- from log, found that openproject use openssl to test connection to nextcloud host.

so I think the problem is SSL Certificate configuration on nextcloud server.

Nextcloud server invalid host="https://my.nextcloud.com" 
error_type=cannot_be_connected_to: 
exception OpenSSL::SSL::SSLError: SSL_connect SYSCALL 
returned=5 errno=0 peeraddr=192.168.x.x:443 
state=error: certificate verify failed

try to use openssl command to manually check.

openssl s_client -showcerts -connect my.nextcloud.com:443 > ./ssl-log.txt

Found that, there was missing Intermediate CA certificate.

*** you need full chain certificate PEM format without key.

in my scenario, 3 certs are needed. which are nextcloud server cert, intermediate CA cert and the root CA cert.

So I make the new full chain PEM, replace the old one on nextcloud server. then restart apache service.

Then I use openssl command to test first.
openssl s_client -showcerts -connect my.nextcloud.com:443 > ./ssl-log.txt

from above command, you'll see message like.

depth=2 C = US, O = DigiCert Inc, OU = www.digicert.com, CN = DigiCert Global Root CA
verify return:1
depth=1 C = US, O = "DigiCert, Inc.", CN = RapidSSL Global TLS RSA4096 SHA256 2022 CA1
verify return:1
depth=0 CN = *.nextcloud.com
verify return:1

You can see, there are 3 certs verified and 'Verify return: 1' that means successful.

Then I go back to File storage admin page. try connect again. DONE !

Same problem here but our nexctcloud uses letsencrypt:

That fixed the problem on my docker container:
https://gist.github.com/Lukas238/a27956da42eae5d082a04fe0f493a9e0