feat(app): implement Google Play App Licensing

Signed-off-by: YuutaW <17158086+Trumeet@users.noreply.github.com>

1 files changed, 31 insertions, 0 deletions

diff --git a/app/src/main/java/moe/yuuta/gplicense/DeviceLimiter.java b/app/src/main/java/moe/yuuta/gplicense/DeviceLimiter.java
new file mode 100644
index 0000000..c2343d9
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+++ b/app/src/main/java/moe/yuuta/gplicense/DeviceLimiter.java
@@ -0,0 +1,31 @@
+package moe.yuuta.gplicense;
+
+/**
+ * Allows the developer to limit the number of devices using a single license.
+ * <p>
+ * The LICENSED response from the server contains a user identifier unique to
+ * the &lt;application, user&gt; pair. The developer can send this identifier
+ * to their own server along with some device identifier (a random number
+ * generated and stored once per application installation,
+ * {@link android.telephony.TelephonyManager#getDeviceId getDeviceId},
+ * {@link android.provider.Settings.Secure#ANDROID_ID ANDROID_ID}, etc).
+ * The more sources used to identify the device, the harder it will be for an
+ * attacker to spoof.
+ * <p>
+ * The server can look at the &lt;application, user, device id&gt; tuple and
+ * restrict a user's application license to run on at most 10 different devices
+ * in a week (for example). We recommend not being too restrictive because a
+ * user might legitimately have multiple devices or be in the process of
+ * changing phones. This will catch egregious violations of multiple people
+ * sharing one license.
+ */
+public interface DeviceLimiter {
+
+    /**
+     * Checks if this device is allowed to use the given user's license.
+     *
+     * @param userId the user whose license the server responded with
+     * @return LICENSED if the device is allowed, NOT_LICENSED if not, RETRY if an error occurs
+     */
+    int isDeviceAllowed(String userId);
+}
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