Openssl : error "self signed certificate in certificate chain"
You have a certificate which is self-signed, so it's non-trusted by default, that's why OpenSSL complains. This warning is actually a good thing, because this scenario might also rise due to a man-in-the-middle attack.
To solve this, you'll need to install it as a trusted server. If it's signed by a non-trusted CA, you'll have to install that CA's certificate as well.
Have a look at this link about installing self-signed certificates.
Here is one-liner to verify certificate to be signed by specific CA:
openssl verify -verbose -x509_strict -CAfile ca.pem certificate.pem
This doesn't require to install CA anywhere.
See How does an SSL certificate chain bundle work? for details and correct certificate chain handling.
If you're running Charles and trying to build a docker container then you'll most likely get this error.
Make sure to disable Charles (macos) proxy under proxy -> macOS proxy
Charles is an
HTTP proxy / HTTP monitor / Reverse Proxy that enables a developer to view all of the HTTP and SSL / HTTPS traffic between their machine and the Internet.
So anything similar may cause the same issue.