Get user's youtube channel id and his youtube subscribtions using Youtube com.google.api.services.youtube.YouTube, no UI.

build.gradle

apply plugin: 'com.android.application'

android {
    compileSdkVersion 26
    defaultConfig {
        applicationId "co.example.youtube"
        minSdkVersion 19
        targetSdkVersion 26
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}
configurations.all {
    resolutionStrategy.force 'com.google.code.findbugs:jsr305:1.3.9'
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'com.android.support:appcompat-v7:26.1.0'
    implementation 'com.android.support.constraint:constraint-layout:1.0.2'
    testImplementation 'junit:junit:4.12'

    compile 'com.google.android.gms:play-services-auth:11.6.0'
    compile 'com.google.api-client:google-api-client-android:1.22.0' exclude module: 'httpclient'
    compile 'com.google.apis:google-api-services-youtube:v3-rev182-1.22.0'
}

MainActivity.java

package co.example.youtube;

/*
Example of how to get user's youtube channel id using google OAuth2,
the app needs to be registered at:
https://console.developers.google.com/apis/
Credentials->Client ID for Android
with the same package name (in this case co.example.youtube)
otherwise error 10 will be received
*/
import android.accounts.Account;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;

import com.google.android.gms.auth.api.Auth;
import com.google.android.gms.auth.api.signin.GoogleSignIn;
import com.google.android.gms.auth.api.signin.GoogleSignInAccount;
import com.google.android.gms.auth.api.signin.GoogleSignInClient;
import com.google.android.gms.auth.api.signin.GoogleSignInOptions;
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.api.ApiException;
import com.google.android.gms.common.api.GoogleApiClient;
import com.google.android.gms.common.api.Scope;
import com.google.android.gms.tasks.Task;
import com.google.api.client.extensions.android.http.AndroidHttp;
import com.google.api.client.googleapis.extensions.android.gms.auth.GoogleAccountCredential;
import com.google.api.client.googleapis.extensions.android.gms.auth.UserRecoverableAuthIOException;
import com.google.api.client.http.HttpTransport;
import com.google.api.client.json.JsonFactory;
import com.google.api.client.json.jackson2.JacksonFactory;

import com.google.api.services.youtube.YouTube;
import com.google.api.services.youtube.model.Channel;
import com.google.api.services.youtube.model.ChannelListResponse;
import com.google.api.services.youtube.model.Subscription;
import com.google.api.services.youtube.model.SubscriptionListResponse;

import java.io.IOException;
import java.util.Collections;
import java.util.List;

/*
Example how to obtain logged user's channel id. You need to register youtube api using package name at:

 */

public class MainActivity extends AppCompatActivity implements GoogleApiClient.OnConnectionFailedListener {

    private static final String TAG = "MainActivity";

    // Scope for reading user's contacts
    private static final String CONTACTS_SCOPE = "https://www.googleapis.com/auth/contacts.readonly";
    private static final String YOUTUBE_SCOPE = "https://www.googleapis.com/auth/youtube";

    // Bundle key for account object
    private static final String KEY_ACCOUNT = "key_account";

    // Request codes
    private static final int RC_SIGN_IN = 9001;
    private static final int RC_RECOVERABLE = 9002;

    private Account mAccount;

    private GoogleApiClient mGoogleApiClient;

    // Global instance of the HTTP transport
    private static final HttpTransport HTTP_TRANSPORT = AndroidHttp.newCompatibleTransport();

    // Global instance of the JSON factory
    private static final JsonFactory JSON_FACTORY = JacksonFactory.getDefaultInstance();

    private GoogleSignInClient mGoogleSignInClient;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
                .requestScopes(new Scope(CONTACTS_SCOPE), new Scope(YOUTUBE_SCOPE))
                .requestEmail()
                .build();

        // Restore instance state
        if (savedInstanceState != null) {
            mAccount = savedInstanceState.getParcelable(KEY_ACCOUNT);
        }
        mGoogleSignInClient = GoogleSignIn.getClient(this, gso);
        // Build a GoogleApiClient with access to the Google Sign-In API and the
        // options specified by gso.
        mGoogleApiClient = new GoogleApiClient.Builder(this)
                .enableAutoManage(this /* FragmentActivity */, this /* OnConnectionFailedListener */)
                .addApi(Auth.GOOGLE_SIGN_IN_API, gso)
                .build();

        signIn();
    }

    @Override
    public void onStart() {
        super.onStart();

        // Check if the user is already signed in and all required scopes are granted
        GoogleSignInAccount account = GoogleSignIn.getLastSignedInAccount(this);
        if (GoogleSignIn.hasPermissions(account, new Scope(CONTACTS_SCOPE), new Scope(YOUTUBE_SCOPE))) {
            Log.d(TAG, "has Permissions");
        } else {
            Log.d(TAG, "NO Permissions");
        }
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putParcelable(KEY_ACCOUNT, mAccount);
    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        // Result returned from launching the Intent from GoogleSignInApi.getSignInIntent(...);
        if (requestCode == RC_SIGN_IN) {
            Task<GoogleSignInAccount> task = GoogleSignIn.getSignedInAccountFromIntent(data);
            handleSignInResult(task);
        }
    }

    private void signIn() {
        Intent signInIntent = mGoogleSignInClient.getSignInIntent();
        startActivityForResult(signInIntent, RC_SIGN_IN);
    }

    private void handleSignInResult(@NonNull Task<GoogleSignInAccount> completedTask) {
        Log.d(TAG, "handleSignInResult:" + completedTask.isSuccessful());

        try {
            GoogleSignInAccount account = completedTask.getResult(ApiException.class);

            // Store the account from the result
            mAccount = account.getAccount();

            // Asynchronously access the Youtube API for the account
            new GetSubscriptionTask().execute(mAccount);

        } catch (ApiException e) {
            Log.w(TAG, "handleSignInResult:error", e);

            // Clear the local account
            mAccount = null;
        }
    }

    /**
     * AsyncTask that uses the credentials from Google Sign In to access Youtube subscription API.
     */
    private class GetSubscriptionTask extends AsyncTask<Account, Void, List<Subscription>> {

        @Override
        protected List<Subscription> doInBackground(Account... params) {
            try {
                GoogleAccountCredential credential = GoogleAccountCredential.usingOAuth2(
                        MainActivity.this,
                        Collections.singleton(YOUTUBE_SCOPE));
                credential.setSelectedAccount(params[0]);

                YouTube youtube = new YouTube.Builder(HTTP_TRANSPORT, JSON_FACTORY, credential)
                        .setApplicationName("Get User's Own Channel")
                        .build();

                ChannelListResponse channelListResponse = youtube.channels().list("id,contentDetails")
                        .setMine(true)
                        .setFields("items(contentDetails/relatedPlaylists/uploads,id)")
                        .execute();

                // get signed user channel id:
                Channel myChannel = channelListResponse.getItems().get(0);
                String channelId = myChannel.getId(); // this is user's channel ID

                Log.d(TAG, "my youtube channel id: " + channelId);

                SubscriptionListResponse connectionsResponse = youtube
                        .subscriptions()
                        .list("snippet")
                        .setChannelId(channelId)
                        .execute();

                return connectionsResponse.getItems();
            } catch (UserRecoverableAuthIOException userRecoverableException) {
                Log.w(TAG, "getSubscription:recoverable exception", userRecoverableException);
                startActivityForResult(userRecoverableException.getIntent(), RC_RECOVERABLE);
            } catch (IOException e) {
                Log.w(TAG, "getSubscription:exception", e);
            }

            return null;
        }

        @Override
        protected void onPostExecute(List<Subscription> subscriptions) {

            if (subscriptions != null) {
                Log.d(TAG, "subscriptions : size=" + subscriptions.size());

                for (Subscription subscription : subscriptions) {
                    Log.v(TAG, "subscription : " + subscription.getId());
                }
            } else {
                Log.d(TAG, "subscriptions: null");
            }
        }
    }
    // MARK: GoogleApiClient.OnConnectionFailedListener
    @Override
    public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {
        // ignore
    }
}

Yeah I was struggling too until find out this, Thanks again 🙂👍🏻 👏🏻👏🏻