Retrofit - OkHTTP Connect to Self signed SSL Enabled Server: (Fix for CertPathValidatorException: Trust Anchor for certificate path not found) - Self Signing Client Bulider for Retrofit OkHTTP

MainActivity.java

public class MainActivity extends AppCompatActivity {
  Retrofit retrofit;
  
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      /*
      Rest
      */
      initNetwork();
  }
  
  private void initNetwork() {
    retrofit = new Retrofit.Builder()
                .baseUrl(Constants.API_BASE_URL)
                .addConverterFactory(GsonConverterFactory.create())
                .client(SelfSigningClientBuilder.createClient(this))
                .build();
                
    /*
     *Do the rest of Retrofit work
     */
  }
}

SelfSigningClientBuilder.java

import android.annotation.SuppressLint;
import android.content.Context;

import java.io.IOException;
import java.io.InputStream;
import java.security.GeneralSecurityException;
import java.security.KeyManagementException;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.security.cert.Certificate;
import java.security.cert.CertificateException;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;

import javax.net.ssl.HostnameVerifier;
import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLSession;
import javax.net.ssl.TrustManager;
import javax.net.ssl.TrustManagerFactory;
import javax.net.ssl.X509TrustManager;

import okhttp3.OkHttpClient;

public class SelfSigningClientBuilder {

    public static OkHttpClient createClient(Context context) {

        OkHttpClient client = null;

        CertificateFactory cf = null;
        InputStream cert = null;
        Certificate ca = null;
        SSLContext sslContext = null;
        try {
            cf = CertificateFactory.getInstance("X.509");
            cert = context.getResources().openRawResource(R.raw.my_cert); // Place your 'my_cert.crt' file in `res/raw`

            ca = cf.generateCertificate(cert);
            cert.close();
            
            String keyStoreType = KeyStore.getDefaultType();
            KeyStore keyStore = KeyStore.getInstance(keyStoreType);
            keyStore.load(null, null);
            keyStore.setCertificateEntry("ca", ca);

            String tmfAlgorithm = TrustManagerFactory.getDefaultAlgorithm();
            TrustManagerFactory tmf = TrustManagerFactory.getInstance(tmfAlgorithm);
            tmf.init(keyStore);

            sslContext = SSLContext.getInstance("TLS");
            sslContext.init(null, tmf.getTrustManagers(), null);

            client = new OkHttpClient.Builder()
                    .sslSocketFactory(sslContext.getSocketFactory())
                    .build();

        } catch (KeyStoreException | CertificateException | NoSuchAlgorithmException | IOException | KeyManagementException e) {
            e.printStackTrace();
        }

        return client;
    }

}

Hello,
Please suggest me to get .crt file

@VinayakMoger @keshavgera @bhargavcode the .crt file is from server which is the public certificate containing the key. You could ask your web developer for that one