how to generate the Security Certificate for client and server of openVPN

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security

Hello Sir,
In order to connect our client and server of openVPN . I need the certificate of authentication for both client and server.

Please tell me how can I generate these certificate.

SERVER: OPENVPN server based on linux.
Keys and Certificate: ca.crt, server.crt, server.key,

CLIENT: OPENVPN client based on Windows.
keys and certificate: ca.key, client.crt, client.key

IF ANYONE WORKING ON THE OPENVPN PLEASE HELPME.