Suddenly all my OpenVPN connections stopped working. Turns out that the signing certificate expired (took some doing to figure this out). Here are some links dealing with OpenVPN certificates (and certificates in general)
How to change CA certificate validity period
OpenVPN - expired certificates
Dumping SSL certificate information
Extend validity of a OpenVPN certificate
Easy-RSA v3 OpenVPN Howto
Easy-TLS
How to decrypt an OpenVPN EasyRSA Encrypted Private Key
Generate OpenVPN Certificates and Keys
For PEM, use the following:
openssl x509 -text -in cert.pem
For PKCS#12, use this:
openssl pkcs12 -info -in cert.pfx
To dump a CSR (Certificate Signing Request), use this:
openssl req -text -in request.csr
To dump/check a private key:
openssl rsa -text -noout -in key.pem