webauthn-kotlin-multiplatform

0.3.0indexed

Standards-first WebAuthn and passkey building blocks: typed protocol models, strict validation, backend ceremony services, client orchestration, and modular transport, storage, crypto and attestation adapters.

AndroidJVMNative·szijpeter/webauthn-kotlin-multiplatform

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WebAuthn Kotlin Multiplatform

Standards-first Kotlin Multiplatform building blocks for WebAuthn and passkey integrations.

This project helps teams implement passwordless login without rebuilding the hardest parts from scratch. It gives you typed protocol models, strict validation, backend ceremony services, platform passkey clients, and optional transport/adaptation modules that stay close to the WebAuthn specification.

Why This Project Exists

WebAuthn is security-sensitive and protocol-heavy.
Passkey products often need to share logic across backend, Android, and iOS.
Kotlin teams usually want typed APIs, predictable validation, and flexible integration points instead of one monolithic SDK.

This repo focuses on those needs:

Standards first: behavior is driven by WebAuthn L3 and related RFCs.
Kotlin-first: KMP modules share the right logic instead of pushing everything into platform wrappers.
Flexible integration: use only the modules you need, from pure model/validation all the way to Ktor routes and client transport helpers.
Heavy lifting included: challenge/origin validation, authenticator-data parsing, signature verification boundaries, attestation policy hooks, and platform bridge logic are already here.

What You Can Build With It

A JVM/Ktor WebAuthn backend using typed ceremony services.
Android and iOS passkey clients with shared Kotlin orchestration.
A client/server setup that shares model and validation semantics instead of duplicating protocol assumptions.
A modular stack where server, client, transport, storage, and attestation trust can be adopted separately.

Sample Recordings

Android	iOS

WebAuthn Core Concepts

WebAuthn has two ceremony pairs:

Registration (create)
Authentication (get)

Each pair has a server start step and a server finish step, with the platform authenticator in the middle.

sequenceDiagram
    autonumber
    actor User
    participant App as Client App
    participant Auth as Platform Authenticator
    participant RP as Relying Party Server

    note over RP,App: Registration ceremony
    App->>RP: registration/start request
    RP-->>App: registration/start response (challenge + options)
    App->>Auth: navigator.credentials.create / platform create
    Auth-->>App: RegistrationResponse
    App->>RP: registration/finish (response + echoed challenge)
    RP-->>App: verified registration

    note over RP,App: Authentication ceremony
    App->>RP: authentication/start request
    RP-->>App: authentication/start response (challenge + options)
    App->>Auth: navigator.credentials.get / platform get
    Auth-->>App: AuthenticationResponse
    App->>RP: authentication/finish (response + echoed challenge)
    RP-->>App: verified sign-in

Validation and trust decisions are server responsibilities: challenge/origin/type checks, authenticator data rules, signature/attestation verification, counter handling, and policy decisions.

Repository structure

The repository follows a layered model that keeps protocol and validation concerns separate from transport and platform adapters.

flowchart TB
    CLIENT["Client stack<br/>Shared orchestration and platform bridges"]
    SERVER["JVM server stack<br/>Ceremonies, storage and HTTP adapters"]
    CRYPTO["Cryptography boundary<br/>Crypto contracts and implementations"]
    FOUNDATION["Shared foundation<br/>Validation, serialization and runtime"]
    MODEL["Protocol model<br/>Typed WebAuthn contracts"]

    CLIENT --> FOUNDATION
    CLIENT --> MODEL
    SERVER --> FOUNDATION
    SERVER --> CRYPTO
    CRYPTO --> FOUNDATION
    FOUNDATION --> MODEL

The overview shows logical responsibility areas rather than every Gradle dependency. See the architecture guide for the reference integration and focused core, client, and server dependency views.

Repository areas

core/ contains reusable protocol, validation, runtime, serialization, and crypto contracts.
client/ contains shared client orchestration, platform bridges, Compose helpers, and client transport.
server/ contains JVM server services, Ktor/store adapters, JVM crypto, and optional trust metadata.
sample/ contains runnable samples and demo entry points; these modules are not published.

Common entry points

How To Read Module Docs

Most module READMEs follow this baseline structure (adapted per module when needed):

What it provides: the module's owned responsibilities.
When to use: where it belongs in an integration.
How to use: practical API snippets plus required caller responsibilities.
How it fits in the system: dependency and data-flow context.

Recommended adoption paths:

Start server-side with model -> core -> crypto-api -> server-core-jvm (+ server-ktor if you want HTTP adapters).
Start client-side with client-core -> platform bridge (+ client-compose for Compose UI).
Add client-prf-crypto only when you need PRF-derived application crypto.

Install

The coordinated release train uses one version for the full published surface. JVM and Android dependency configurations can use the BOM; Kotlin Multiplatform common and Native source sets should put that same version on each artifact because Java Platform constraints are not available to Native variants.

repositories {
    google()
    mavenCentral()
}

Use only the modules your app actually wires in. In Kotlin Multiplatform projects, shared modules belong in commonMain, while concrete platform bridges belong in the matching platform source set.

Client-side KMP example:

kotlin {
    sourceSets {
        commonMain.dependencies {
            implementation("io.github.szijpeter:webauthn-client-core:<version>")
            implementation("io.github.szijpeter:webauthn-network-ktor-client:<version>")
        }

        androidMain.dependencies {
            implementation("io.github.szijpeter:webauthn-client-android:<version>")
        }

        iosMain.dependencies {
            implementation("io.github.szijpeter:webauthn-client-ios:<version>")
        }
    }
}

JVM/Ktor server example:

dependencies {
    implementation(platform("io.github.szijpeter:webauthn-bom:<version>"))
    implementation("io.github.szijpeter:webauthn-server-core-jvm")
    implementation("io.github.szijpeter:webauthn-server-jvm-crypto")
    implementation("io.github.szijpeter:webauthn-server-ktor")
}

Notes:

Published to Maven Central (latest version is shown in the Maven Central badge above). Maintainers can still validate publication locally with:

./gradlew publishToMavenLocal --stacktrace

Quick Start Paths

Server-first

Use:

Client-first

Use:

End-to-end reference app

Start with:

sample/backend-ktor
sample/compose-passkey
sample/compose-passkey-ios
sample/passkey-cli for a macOS-first experimental native-authenticator CLI POC

Desktop and CLI strategy notes for this repo live in docs/DESKTOP_CLI_STRATEGY.md.

Public Modules

Status and Current Limits

This repository is publicly released and still pre-1.0.

Current state:

Core/server validation paths are production-leaning.
Publish/release infrastructure is now wired for Maven Central and compatibility baselines.
Client flows are usable on Android and iOS with shared orchestration.
iOS external security-key support is still being hardened before it can be documented as fully ready.
kotlinx-serialization is now on 1.10.0 together with Signum 0.12.0 and indispensable ; captured Android assertion-vector regressions are green on this combined dependency set.

Security and Release Hygiene

Vulnerability reporting: see SECURITY.md.
Public-launch checklist: docs/PUBLIC_LAUNCH_CHECKLIST.md.
Maven Central maintainer guide: .

Maintainer Workflow

tools/agent/setup-hooks.sh
tools/agent/quality-gate.sh --mode fast --scope changed --block false
tools/agent/quality-gate.sh --mode strict --scope changed --block false
./gradlew apiCheck --stacktrace
./gradlew publishToMavenLocal --stacktrace

Related Docs

License: Apache-2.0. See LICENSE.

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`platform:bom`	Consumers who want aligned versions across published artifacts
`webauthn-cbor-core`	Parser/crypto modules needing strict low-level CBOR byte scanning primitives
`webauthn-model`	Teams that want typed WebAuthn models and value wrappers
`webauthn-runtime-core`	Shared coroutine-safe error/cancellation boundary helpers for adapter modules
`webauthn-serialization-kotlinx`	Teams mapping JSON/CBOR DTOs to typed models
`webauthn-core`	Teams validating ceremonies and authenticator data
`webauthn-crypto-api`	Teams plugging crypto/attestation implementations into validation and server flows
`webauthn-server-jvm-crypto`	JVM backends that want Signum-first hashing, signature, and attestation verification
`webauthn-server-core-jvm`	JVM backends that need registration/authentication ceremony services
`webauthn-server-ktor`	Ktor backends that want ready-made WebAuthn routes
`webauthn-server-store-exposed`	JVM backends storing WebAuthn state through Exposed
`webauthn-client-core`	Shared passkey orchestration and controller-driven flows
`webauthn-client-json-core`	Apps or SDKs that need raw JSON interoperability on top of typed clients
`webauthn-client-compose`	Compose apps that want remembered client/controller helpers
`webauthn-client-android`	Android apps using Credential Manager
`webauthn-client-ios`	iOS apps using AuthenticationServices
`webauthn-client-prf-crypto`	Client apps deriving crypto sessions from WebAuthn PRF extension outputs
`webauthn-network-ktor-client`	Clients talking to a `/webauthn/*` backend contract over Ktor (`HttpClient` contract + caller-selected engine)
`webauthn-attestation-mds`	Backends that want optional FIDO Metadata Service trust anchors