Validate server-side verification (SSV) callbacks

Page Summary

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• Server-side verification callbacks notify an external system to reward a user for interacting with a rewarded ad, offering increased protection against spoofing compared to client-side methods.

• This guide demonstrates verifying rewarded SSV callbacks using the Tink Java Apps library, though any third-party library supporting ECDSA can be used.

• Rewarded SSV callbacks include various query parameters providing details about the ad interaction, including the ad unit, reward amount, and transaction ID.

• Public keys required for verification can be fetched from the AdMob key server and should be cached but not for longer than 24 hours due to regular rotation.

• The verification process involves parsing the callback URL to get the content to be verified, the signature, and the key ID, then using the appropriate public key to verify the signature against the content.

Server-side verification callbacks are URL requests, with query parameters expanded by Google, that are sent by Google to an external system to notify it that a user should be rewarded for interacting with a rewarded or rewarded interstitial ad. Rewarded SSV (server-side verification) callbacks provide an extra layer of protection against spoofing of client-side callbacks to reward users.

This guide shows you how to verify rewarded SSV callbacks by using the Tink Java Apps third-party cryptographic library to ensure that the query parameters in the callback are legitimate values. Although Tink is used for the purposes of this guide, you have the option to use any third-party library that supports ECDSA. You can also test your server with the testing tool in the AdMob UI.

Prerequisites

• Enable rewarded server-side verification on your ad unit.

Use RewardedAdsVerifier from the Tink Java Apps library

The Tink Java Apps GitHub repository includes a RewardedAdsVerifier helper class to reduce the code required to verify a rewarded SSV callback. Using this class enables you to verify a callback URL with the following code.

RewardedAdsVerifier verifier = new RewardedAdsVerifier.Builder()
    .fetchVerifyingPublicKeysWith(
        RewardedAdsVerifier.KEYS_DOWNLOADER_INSTANCE_PROD)
    .build();
String rewardUrl = ...;
verifier.verify(rewardUrl);

If the verify() method executes without raising an exception, the callback URL was successfully verified. The Rewarding the user section details best practices regarding when users should be rewarded. For a breakdown of the steps performed by this class to verify rewarded SSV callbacks, you can read through the Manual verification of rewarded SSV section.

SSV callback parameters

Server-side verification callbacks contain query parameters that describe the rewarded ad interaction. Parameter names, descriptions, and example values are listed below. Parameters are sent in alphabetical order.

Ad source identifiers