Add Magistrate to Your Android App

The Magistrate module sits on top of the Octet Mobile SDK. One call, decide, fetches your policy, makes the location proofs it needs, and returns the engine's signed decision.

Prerequisites

• Android minSdk 30 or later, the Octet Mobile SDK's minimum.
• The Octet Mobile SDK set up in your app, with the ACCESS_FINE_LOCATION permission. Follow the Android Quickstart first.
• A release-signed build on a real device for production. A debug build or an emulator needs a sandbox token.
• A policy published from the Magistrate studio.

1. Add the dependency

Add the Magistrate Maven repository and the dependency. Magistrate brings in the Octet SDK (com.octetproof:sdk, 3.0.0 or later) for you.

// settings.gradle.kts
dependencyResolutionManagement {
    repositories {
        maven("https://raw.githubusercontent.com/octetproof/octet-magistrate-android/mvn-repo")
    }
}

// app/build.gradle.kts
dependencies {
    implementation("com.octetproof:magistrate:0.1.0")
}

2. Start the SDK and wrap it

import com.octetproof.magistrate.Magistrate
import com.octetproof.sdk.api.Octet
import com.octetproof.sdk.api.OctetConfig

val config = OctetConfig(licenseKey = "")   // required by the type, ignored by start
val sdk = Octet.start(context = applicationContext, config = config)
val magistrate = Magistrate(sdk)

To keep the verified policy across launches, pass a store:

val magistrate = Magistrate(sdk, persistentStore = EncryptedPrefsPolicyBundleStore(context))

3. Ask for a decision

Call decide when the user does something your policy protects, such as opening an account or placing a bet. It is a suspend function.

val license = sdk.licenseStatus ?: return

try {
    val result = magistrate.decide(license)
    if (result.cause != null) {
        // UNKNOWN: the location couldn't be settled, for example no fix yet.
        // Ask the user to retry.
    }
    // Send result.receipt to your backend with the request.
    // Your backend verifies it and decides what happens.
    api.submit(order, decisionReceipt = result.receipt)
} catch (e: PolicyException) {
    // No decision was made. Treat it as NO.
}

decide runs the whole exchange: it fetches the policy, checks Octet's signature on it, gets a one-time challenge, has the SDK make the proofs, and sends them to the engine. Don't manage the challenge yourself, unless your backend starts the check (see Start the check from your backend).

A deny is a result, not an error. result.isPermit is false and result.reasons says why. When result.cause is set, the answer is UNKNOWN: the proofs couldn't settle the location. A PolicyException means no decision was made at all. See Decision Response to read a result as YES, NO or UNKNOWN.

Several policies in one check

decideMany decides up to 16 policies with one set of proofs. Each result carries its policy's name.

val set = magistrate.decideMany(license, policies = listOf("p_…", "p_…"))
set.results.forEach { println("${it.policy} ${it.decision}") }

Obligations

A policy can attach obligations to a permit, for example a step-up authentication. A permit with obligations counts only once your app and backend have fulfilled every one. Treat an obligation you don't recognise as NO. See Decision Response.

Things to know

• The first check after start. Location takes a moment to warm up after Octet.start. The first check can come back UNKNOWN, with cause absence. Retry after a few seconds.
• Real devices for production. Production needs hardware attestation on a real device with a release-signed build. An emulator or a debug build signs in with a sandbox token (see the Android Quickstart), and its results and receipts say env sandbox. Your backend accepts only prod in production. Magistrate checks from a sandbox build need Octet SDK 3.1.0 or later, and a sandbox app registered on your license. Production apps don't.
• Geofence policies. A policy with a disc needs an Octet SDK release that can prove one. Until then decide throws BindingUnavailable for it. Policies from the Magistrate studio don't use discs.
• Errors. See Errors for each PolicyException case.

Sample app

The sample app starts the SDK, calls decide and shows the decision, reasons and obligations. It needs a real device and a release-signed build.