How to do an HTTPS POST from Android?

You can use the default CAs that are defined in the android device, which is just fine for any public web.

If you have a self-signed certificate, you can either accept all certificates (risky, open to man-in-the-middle attacks) or create your own TrustManagerFactory, which is a bit out of this scope.

Here’s some code to use the default CAs for a https POST call:

private InputStream getInputStream(String urlStr, String user, String password) throws IOException
{
    URL url = new URL(urlStr);
    HttpsURLConnection conn = (HttpsURLConnection) url.openConnection();

    // Create the SSL connection
    SSLContext sc;
    sc = SSLContext.getInstance("TLS");
    sc.init(null, null, new java.security.SecureRandom());
    conn.setSSLSocketFactory(sc.getSocketFactory());
      
    // Use this if you need SSL authentication
    String userpass = user + ":" + password;
    String basicAuth = "Basic " + Base64.encodeToString(userpass.getBytes(), Base64.DEFAULT);
    conn.setRequestProperty("Authorization", basicAuth);
    
    // set Timeout and method
    conn.setReadTimeout(7000);
    conn.setConnectTimeout(7000);
    conn.setRequestMethod("POST");
    conn.setDoInput(true);
    
    // Add any data you wish to post here
    
    conn.connect();
    return conn.getInputStream();
}   

To read the response:

String result = new String();
InputStream is = getInputStream(urlStr, user, password);
BufferedReader in = new BufferedReader(new InputStreamReader(is));
String inputLine;
while ((inputLine = in.readLine()) != null) {
    result += inputLine;            
}