Install a certificate for opening site inside a Webview?

Question

I have a website which I want to open in an Android Webview. The website uses a certificate emitted by COMODO RSA Domain Validation Secure Server CA. The problem is that I get an Unkown Certificate Error for devices all running a version less than (including) Android 5.

I serched in the documentation and as far as I understood the problem is that the CA was created before the release of Android 5.

I could do a handler.proceed(); on onReceivedSslError but I want to keep the app secure and I think Google can reject the app on play store anyway.

I found that I cound do something like this

// Load CAs from an InputStream
// (could be from a resource or ByteArrayInputStream or ...)
CertificateFactory cf = CertificateFactory.getInstance("X.509");
// From https://www.washington.edu/itconnect/security/ca/load-der.crt
InputStream caInput = new BufferedInputStream(new FileInputStream("load-der.crt"));
Certificate ca;
try {
    ca = cf.generateCertificate(caInput);
    System.out.println("ca=" + ((X509Certificate) ca).getSubjectDN());
} finally {
    caInput.close();
}

// Create a KeyStore containing our trusted CAs
String keyStoreType = KeyStore.getDefaultType();
KeyStore keyStore = KeyStore.getInstance(keyStoreType);
keyStore.load(null, null);
keyStore.setCertificateEntry("ca", ca);

// Create a TrustManager that trusts the CAs in our KeyStore
String tmfAlgorithm = TrustManagerFactory.getDefaultAlgorithm();
TrustManagerFactory tmf = TrustManagerFactory.getInstance(tmfAlgorithm);
tmf.init(keyStore);

// Create an SSLContext that uses our TrustManager
SSLContext context = SSLContext.getInstance("TLS");
context.init(null, tmf.getTrustManagers(), null);

// Tell the URLConnection to use a SocketFactory from our SSLContext
URL url = new URL("https://certs.cac.washington.edu/CAtest/");
HttpsURLConnection urlConnection =
    (HttpsURLConnection)url.openConnection();
urlConnection.setSSLSocketFactory(context.getSocketFactory());
InputStream in = urlConnection.getInputStream();
copyInputStreamToOutputStream(in, System.out);

but the problem is that my code is like so

myWebView.loadUrl("https://site.domain.com")

How can I install the certificate of the CA within my Webview?

Thanks