> For the complete documentation index, see [llms.txt](https://azutopia.gitbook.io/authly/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://azutopia.gitbook.io/authly/readme.md).

# Welcome to Authly

Production-ready OAuth 2.0, OpenID Connect, and FAPI authentication library for Crystal.

**Authly** is a strongly-typed, zero-framework Crystal shard for building **OAuth 2.0**, **OpenID Connect (OIDC)**, and **Financial-grade API (FAPI)** Authorization Servers and Resource Servers on top of Crystal's standard `HTTP::Handler`.

***

## Documentation Sections

<table data-view="cards"><thead><tr><th></th><th></th><th data-hidden data-card-target data-type="content-ref"></th></tr></thead><tbody><tr><td><strong>🎓 Tutorials</strong></td><td>Step-by-step guided lessons that take you from a blank Crystal project to a working OAuth2 server and protected API.</td><td><a href="/authly/tutorials/tutorials.md">Overview</a></td></tr><tr><td><strong>🛠️ How-To Guides</strong></td><td>Goal-oriented recipes for Redis stores, scope enforcement, PAR, JARM, mTLS, key rotation, and Dynamic Client Registration.</td><td><a href="/authly/how-to-guides/how-to.md">Overview</a></td></tr><tr><td><strong>📖 Reference</strong></td><td>Complete technical specifications for <code>Authly::Configuration</code>, HTTP endpoints, Crystal interfaces, and error codes.</td><td><a href="/authly/reference/reference.md">Overview</a></td></tr><tr><td><strong>💡 Explanation</strong></td><td>Deep dives into Authly's architecture, refresh token rotation families, atomic single-use credentials, and threat model.</td><td><a href="/authly/explanation/explanation.md">Overview</a></td></tr></tbody></table>

***

## Quick Installation

{% tabs %}
{% tab title="shard.yml" %}

```yaml
dependencies:
  authly:
    github: azutoolkit/authly
```

{% endtab %}

{% tab title="Terminal" %}

```bash
shards install
```

{% endtab %}
{% endtabs %}

***

## Capabilities at a Glance

| Category                | Supported Specifications & Features                                                                                                                                                                                                                                                                                                                                         |
| ----------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **OAuth 2.0 Grants**    | Authorization Code (`authorization_code`), PKCE (`S256` / `plain`), Client Credentials (`client_credentials`), Refresh Token (`refresh_token`), Device Authorization (`urn:ietf:params:oauth:grant-type:device_code`), Cryptographic Challenge-Response (`challenge_response` / `urn:ietf:params:oauth:grant-type:challenge`), Password (`password`), Implicit (`implicit`) |
| **OpenID Connect**      | ID Tokens, UserInfo Endpoint (`/oauth/userinfo`), OIDC Discovery (`/.well-known/openid-configuration`), RFC 8414 Metadata (`/.well-known/oauth-authorization-server`), JWKS (`/.well-known/jwks.json`)                                                                                                                                                                      |
| **FAPI & Hardening**    | Pushed Authorization Requests (PAR / RFC 9126), JWT Secured Authorization Response Mode (JARM / RFC 9101), Certificate-Bound mTLS Tokens (`cnf.x5t#S256` / RFC 8705), Dynamic Client Registration (RFC 7591)                                                                                                                                                                |
| **Resource Protection** | `Authly::Handler::Bearer` (RFC 6750), `Authly::Handler::RequireScope` (`all` / `any`), Audience (`aud`) verification, JWT & Opaque token strategies                                                                                                                                                                                                                         |

***

## Start Building

{% content-ref url="/pages/AByNuSoPCgmfM08w1pFQ" %}
[Getting Started: First OAuth2 Server & API](/authly/tutorials/tutorials/getting-started.md)
{% endcontent-ref %}

{% content-ref url="/pages/JkNZo004axXaA91S5l39" %}
[Cryptographic Challenge-Response Auth](/authly/tutorials/tutorials/challenge-response-auth.md)
{% endcontent-ref %}


---

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