cURL error 28: NSS: client certificate not found (nickname not specified)

[ghnp5]

• [x] I have read the README entirely
• [x] I have verified in the issues that my problem hasn't already been resolved

Setup

• Operating System: CentOS 7
• PHP Version: 8.1
• web-push-php Version: 7.0.0

Please check that you have installed and enabled these PHP extensions :

• [x] gmp
• [x] mbstring
• [x] curl
• [x] openssl

Problem

Occasionally, I'm seeing this error being reported when trying to send Push Notifications:

cURL error 28: NSS: client certificate not found (nickname not specified) (see https://curl.haxx.se/libcurl/c/libcurl-errors.html)

only for endpoints starting with:

https://****.notify.windows.com/w/?token=

Expected

Hopefully we wouldn't see an error. I'm not sure what is causing this.

Features Used

• [x] VAPID Support
• [x] Sending with Payload