Where is the signature of CERT.SF on CERT.RSA (Android)

I want to verify android apk signature. (not using jarsigner lib.) So, I have a plan like this:

• Getting public key from apk.
• Getting CERT.SF signature from apk
• Verification of the public key signature of 1.

I can get the public key from CERT.RSA using an openssl command like this. (- openssl pkcs7 -inform DER -in CERT.RSA -noout -print_certs -text)

But how can I get the CERT.SF signature in the CERT.RSA file.

If anyone knows how to get this, let me know. That would be helpful to me. Thank!