Use a certificate in an okhttp request with android

Question

The server of the application in which I work uses a certificate to allow requests. I have it installed, for example, in the desktop Chrome browser and it works fine. It´s a usual certificate with the extension .cer

Now I have to make this certificate work also in my android application and, honestly, I have never done it and I'm a bit lost.

To make the requests I am using okhttp2, as you can see in this example:

 public String makeServiceCall(String url, JSONObject data) {
        final MediaType JSON = MediaType.parse("application/json; charset=utf-8");
        OkHttpClient client = new OkHttpClient();
        client.setConnectTimeout(45, TimeUnit.SECONDS);
        client.setReadTimeout(45, TimeUnit.SECONDS);
        client.setProtocols(Arrays.asList(Protocol.HTTP_1_1));

        RequestBody body = RequestBody.create(JSON, data.toString());
        Request request = new Request.Builder()
                .url(url)
                .header("Accept","application/json")
                .post(body)
                .build();
        try {
            Response response = client.newCall(request).execute();
            return response.body().string();
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
    }

So far everything works perfectly, but after searching and reading tutorials, examples, etc, (many of them from this page) I have not managed to make it work. Make it work with the certificate.

Having never done this, and being a bit confused already, I would appreciate the following clarifications:

• The certificate in .cer format that I have, I suppose I should convert it to another format to be able to use it in android ... Is it correct? If it is correct, how should I do it?

ok, I already have my certificate converted to BKS and hosted in the res / raw folder, but I'm still unable to apply it successfully to the request okhttp2 ..

• Once with a certificate in correct format, How is it implemented with the requests that I am already making in the code that I have set as an example?

I have searched for information about doing it using okhttp3 but I have not been able to authorize the requests either.

This article has been useful to me, but I am not using retrofit and adapting it to okhttp2 does not work either.

I would appreciate an explanation of how to do it

Answer 1

Here is an implementation using official okhttp3 sample code. It is possible to create a trusted OkHttpClient using a custom certificate. I've put the .cer certificate in res/raw then read it in using the trustedCertificatesInputStream() method.

CustomTrust customTrust = new CustomTrust(getApplicationContext());
OkHttpClient client = customTrust.getClient();

CustomTrust.java

import android.content.Context;

import java.io.IOException;
import java.io.InputStream;
import java.security.GeneralSecurityException;
import java.security.KeyStore;
import java.security.cert.Certificate;
import java.security.cert.CertificateFactory;
import java.util.Arrays;
import java.util.Collection;

import javax.net.ssl.KeyManagerFactory;
import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLSocketFactory;
import javax.net.ssl.TrustManager;
import javax.net.ssl.TrustManagerFactory;
import javax.net.ssl.X509TrustManager;

import okhttp3.CertificatePinner;
import okhttp3.OkHttpClient;

public final class CustomTrust {

    private final OkHttpClient client;
    private final Context context;

    public CustomTrust(Context context) {

        this.context = context;
        X509TrustManager trustManager;
        SSLSocketFactory sslSocketFactory;
        try {
            trustManager = trustManagerForCertificates(trustedCertificatesInputStream());
            SSLContext sslContext = SSLContext.getInstance("TLS");
            sslContext.init(null, new TrustManager[]{trustManager}, null);
            sslSocketFactory = sslContext.getSocketFactory();
        } catch (GeneralSecurityException e) {
            throw new RuntimeException(e);
        }

        client = new OkHttpClient.Builder()
                .sslSocketFactory(sslSocketFactory, trustManager)
                .connectTimeout(45, TimeUnit.SECONDS)
                .readTimeout(45, TimeUnit.SECONDS)
                .protocols(Arrays.asList(Protocol.HTTP_1_1))
                .build();
    }

    public OkHttpClient getClient() {
        return client;
    }

    /**
     * Returns an input stream containing one or more certificate PEM files. This implementation just
     * embeds the PEM files in Java strings; most applications will instead read this from a resource
     * file that gets bundled with the application.
     */
    private InputStream trustedCertificatesInputStream() {
        return context.getResources().openRawResource(R.raw.certificate);
    }

    /**
     * Returns a trust manager that trusts {@code certificates} and none other. HTTPS services whose
     * certificates have not been signed by these certificates will fail with a {@code
     * SSLHandshakeException}.
     *
     * <p>This can be used to replace the host platform's built-in trusted certificates with a custom
     * set. This is useful in development where certificate authority-trusted certificates aren't
     * available. Or in production, to avoid reliance on third-party certificate authorities.
     *
     * <p>See also {@link CertificatePinner}, which can limit trusted certificates while still using
     * the host platform's built-in trust store.
     *
     * <h3>Warning: Customizing Trusted Certificates is Dangerous!</h3>
     *
     * <p>Relying on your own trusted certificates limits your server team's ability to update their
     * TLS certificates. By installing a specific set of trusted certificates, you take on additional
     * operational complexity and limit your ability to migrate between certificate authorities. Do
     * not use custom trusted certificates in production without the blessing of your server's TLS
     * administrator.
     */
    private X509TrustManager trustManagerForCertificates(InputStream in)
            throws GeneralSecurityException {
        CertificateFactory certificateFactory = CertificateFactory.getInstance("X.509");
        Collection<? extends Certificate> certificates = certificateFactory.generateCertificates(in);
        if (certificates.isEmpty()) {
            throw new IllegalArgumentException("expected non-empty set of trusted certificates");
        }

        // Put the certificates a key store.
        char[] password = "password".toCharArray(); // Any password will work.
        KeyStore keyStore = newEmptyKeyStore(password);
        int index = 0;
        for (Certificate certificate : certificates) {
            String certificateAlias = Integer.toString(index++);
            keyStore.setCertificateEntry(certificateAlias, certificate);
        }

        // Use it to build an X509 trust manager.
        KeyManagerFactory keyManagerFactory = KeyManagerFactory.getInstance(
                KeyManagerFactory.getDefaultAlgorithm());
        keyManagerFactory.init(keyStore, password);
        TrustManagerFactory trustManagerFactory = TrustManagerFactory.getInstance(
                TrustManagerFactory.getDefaultAlgorithm());
        trustManagerFactory.init(keyStore);
        TrustManager[] trustManagers = trustManagerFactory.getTrustManagers();
        if (trustManagers.length != 1 || !(trustManagers[0] instanceof X509TrustManager)) {
            throw new IllegalStateException("Unexpected default trust managers:"
                    + Arrays.toString(trustManagers));
        }
        return (X509TrustManager) trustManagers[0];
    }

    private KeyStore newEmptyKeyStore(char[] password) throws GeneralSecurityException {
        try {
            KeyStore keyStore = KeyStore.getInstance(KeyStore.getDefaultType());
            InputStream in = null; // By convention, 'null' creates an empty key store.
            keyStore.load(in, password);
            return keyStore;
        } catch (IOException e) {
            throw new AssertionError(e);
        }
    }

}

Answer 2

Although an answer has already been provided, which is good and works perfect, I would like to provide an alternative which requires less custom code.

InputStream trustedCertificatesAsInputStream = context.getResources().openRawResource(R.raw.certificate);
List<Certificate> trustedCertificates = CertificateUtils.loadCertificate(trustedCertificatesAsInputStream);

SSLFactory sslFactory = SSLFactory.builder()
          .withTrustMaterial(trustedCertificates)
          .build();

SSLSocketFactory sslSocketFactory = sslFactory.getSslSocketFactory();
X509ExtendedtrustManager trustManager = sslFactory.getTrustManager().orElseThrow();

OkHttpClient okHttpClient = OkHttpClient.Builder()
          .sslSocketFactory(sslSocketFactory, trustManager)
          .build();

The above library is maintained by me and you can find it here: GitHub - SSLContext Kickstart