How does google verify Android SHA1 fingerprints and packages?

Question

I am trying to make my Google Translate API work but currently I can't find a way. This is how I have set things in Google Developer Console :
I have set my SHA1 fingerprint with the debug certificates. And package name -"bg.webmap.wordy"(which is the actual name). When I try to make a call an "ipRefererBlocked" error is returned in JSON. But when I remove the fingerprint and package name, It works perfectly, but then everybody can use this key, so it is very insecure. So my problem is with authentication.
Will my app automatically send this fingerprint when the API is called? Should I send it myself and how? May the problem be in the debug certificates?

Answer 1

Will my app automatically send this fingerprint when the API is called?

NO!

Should I send it myself and how?

YES!

When setting up your API key restriction for android app, you specified the package name and SHA-1 certificate fingerprint. So when you send an request to Google, you must add these information in the header of each request.

HOW?

As answered here, you need to get your package name and SHA certificate from your code, and then adding to request header.

Get SHA certificate:

/**
 * Gets the SHA1 signature, hex encoded for inclusion with Google Cloud Platform API requests
 *
 * @param packageName Identifies the APK whose signature should be extracted.
 * @return a lowercase, hex-encoded
 */
public static String getSignature(@NonNull PackageManager pm, @NonNull String packageName) {
    try {
        PackageInfo packageInfo = pm.getPackageInfo(packageName, PackageManager.GET_SIGNATURES);
        if (packageInfo == null
                || packageInfo.signatures == null
                || packageInfo.signatures.length == 0
                || packageInfo.signatures[0] == null) {
            return null;
        }
        return signatureDigest(packageInfo.signatures[0]);
    } catch (PackageManager.NameNotFoundException e) {
        return null;
    }
}

private static String signatureDigest(Signature sig) {
    byte[] signature = sig.toByteArray();
    try {
        MessageDigest md = MessageDigest.getInstance("SHA1");
        byte[] digest = md.digest(signature);
        return BaseEncoding.base16().lowerCase().encode(digest);
    } catch (NoSuchAlgorithmException e) {
        return null;
    }
}

Adding to request header:

java.net.URL url = new URL(REQUEST_URL);
HttpURLConnection connection = (HttpURLConnection)url.openConnection();
try {
    connection.setDoInput(true);
    connection.setDoOutput(true);

    connection.setRequestProperty("Content-Type", "application/json; charset=UTF-8");
    connection.setRequestProperty("Accept", "application/json");

    // add package name to request header
    String packageName = mActivity.getPackageName();
    connection.setRequestProperty("X-Android-Package", packageName);
    // add SHA certificate to request header
    String sig = getSignature(mActivity.getPackageManager(), packageName);
    connection.setRequestProperty("X-Android-Cert", sig);
    connection.setRequestMethod("POST");

    // ADD YOUR REQUEST BODY HERE
    // ....................
} catch (Exception e) {
    e.printStackTrace();
} finally {
    connection.disconnect();
}

You can see full answer here.

Enjoy coding :)