Why Does My TLS Connection Fail with a Self-Signed Certificate and How Can I Fix It?

Troubleshooting TLS Connections with Self-Signed Certificates

Issue: Establishing a TLS connection using a self-signed server certificate fails with an error indicating an unknown certificate authority.

Relevant Code:
Client:

CA_Pool := x509.NewCertPool()
severCert, err := ioutil.ReadFile("./cert.pem")
CA_Pool.AppendCertsFromPEM(severCert)

config := tls.Config{RootCAs: CA_Pool}

Server:

cert, err := tls.LoadX509KeyPair("./cert.pem", "./key.pem")
config := tls.Config{Certificates: []tls.Certificate{cert}}

Error Message:

client: dial: x509: certificate signed by unknown authority 
(possibly because of "x509: invalid signature: parent certificate
cannot sign this kind of certificate" while trying to verify 
candidate authority certificate "serial:0")

Root Cause:
The self-signed certificate generated does not have the IsCA flag set, indicating that it is not an intermediate or root certificate. Consequently, the CA Pool of the client is unable to verify the self-signed certificate as a valid authority.

Solution:
To rectify this issue, ensure that the IsCA flag is set when generating the self-signed certificate using x509.CreateCertificate. The correct code for certificate generation is as follows:

certTemplate := &x509.Certificate{
    IsCA: true,
    KeyUsage: x509.KeyUsageCertSign,
    // ... other certificate parameters
}

By setting IsCA:true, the self-signed certificate can properly serve as a certificate authority, enabling the client to verify its authenticity.

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