Getting certificate details from an apk
Try the following:
openssl pkcs7 -inform DER -in CERT.RSA -noout -print_certs -text
unzip -p Name-of-apk.apk META-INF/CERT.RSA | keytool -printcert is what I used .
It produces information such as the owner, issuer, serial number, valid through, certificate fingerprints, signature algorithms and version.
The easiest of all:
keytool -printcert -jarfile file.apk
This also works for Android App Bundles (.aab)