[ruby/openssl] pkey: add PKey#inspect and #oid

Implement OpenSSL::PKey::PKey#oid as a wrapper around EVP_PKEY_id().
This allows user code to check the type of a PKey object.

EVP_PKEY can have a pkey type for which we do not provide a dedicated
subclass. In other words, an EVP_PKEY that is not any of {RSA,DSA,DH,EC}
can exist. It is currently not possible to distinguish such a pkey.

Also, implement PKey#inspect to include the key type for convenience.

dafbb1b3e6

test/openssl/test_pkey.rb

@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+require_relative "utils"
+
+class OpenSSL::TestPKey < OpenSSL::PKeyTestCase
+  def test_generic_oid_inspect
+    # RSA private key
+    rsa = Fixtures.pkey("rsa-1")
+    assert_instance_of OpenSSL::PKey::RSA, rsa
+    assert_equal "rsaEncryption", rsa.oid
+    assert_match %r{oid=rsaEncryption}, rsa.inspect
+
+    # X25519 private key
+    x25519_pem = <<~EOF
+    -----BEGIN PRIVATE KEY-----
+    MC4CAQAwBQYDK2VuBCIEIHcHbQpzGKV9PBbBclGyZkXfTC+H68CZKrF3+6UduSwq
+    -----END PRIVATE KEY-----
+    EOF
+    begin
+      x25519 = OpenSSL::PKey.read(x25519_pem)
+    rescue OpenSSL::PKey::PKeyError
+      # OpenSSL < 1.1.0
+      pend "X25519 is not implemented"
+    end
+    assert_instance_of OpenSSL::PKey::PKey, x25519
+    assert_equal "X25519", x25519.oid
+    assert_match %r{oid=X25519}, x25519.inspect
+  end
+end