Get the public key from an HTTP server in Android

Question

I would like to fetch the RSA public key from an HTTPS server in my Android app.

I don't care wether it is valid or not.

Ideally; I would like to be able to extract infos about the whole certificate chain.

How to achieve this?

Answer 1

It's actually trivial.

val url = URL(BASE_WEB_ENDPOINT_PRIMARY)
val connection: HttpsURLConnection = url.openConnection() as HttpsURLConnection
connection.connect()
connection.serverCertificates.forEach {
  it.publicKey // <== the public key
}