APIac

APIac: API access control for elixir

APIac is a standard interface for API access control and is composed of:

• APIac.Authenticator: an Elixir behaviour for API authentication plugs
• APIac.Filter: an Elixir behaviour for API filter plugs
• Convenience functions for working with APIac plugs and for HTTP APIs

The following APIac plugs are available:

• APIac.Authenticator:

  • APIacAuthBasic: implementatoin of the Basic HTTP authentication scheme (RFC7617)
  • APIacAuthBearer: implementation of the Bearer HTTP authentication scheme (RFC6750) and the OAuth 2.0 Token Introspection (RFC7662) token verification method
  • APIacAuthMTLS: implementation of the OAuth 2.0 Mutual TLS Client Authentication and Certificate Bound Access Tokens RFC8705
  • APIacAuthClientJWT: implementation of the client authentication part of RFC7523 (JSON Web Token (JWT) Profile for OAuth 2.0 Client Authentication and Authorization Grants)
  • APIacAuthClientSecretPost: implementation of the OAuth2 client secret post scheme

• APIac.Filter:

  • APIacFilterIPWhitelist: IPv4 and IPv6 address whitelisting
  • APIacFilterIPBlacklist: IPv4 and IPv6 address blacklisting
  • APIacFilterThrottler: throttler that can throttle on IP address, client, subject, URI, etc.

Usage

Just use one or more of these aforementioned APIac plugs, this library will be automatically imported.

Chaining plugs

APIac interfaces are designed so that you can chain APIac plugs. Example:

my_app/lib/my_app_web/router.ex

pipeline :api_public do
  plug APIacAuthBasic,
    realm: "Public API",
    callback: &MyApp.get_client_secret/2,
    set_error_response: APIacAuthBasic.set_WWWauthenticate_header/3,
    error_response_verbosity: :debug},
  plug APIacAuthBearer,
    bearer_validator:
      {APIacAuthBearer.Validator.Introspect, [
        issuer: "https://example.com/auth"
        tesla_middleware:[
          {Tesla.Middleware.BasicAuth, [username: "client_id_123", password: "WN2P3Ci+meSLtVipc1EZhbFm2oZyMgWIx/ygQhngFbo"]}
        ]]},
    bearer_extract_methods: [:header, :body],
    required_scopes: ["article:write", "comments:moderate"],
    forward_bearer: true,
    cache: {APIacAuthBearerCacheCachex, []}
  plug APIacFilterThrottler,
    key: &APIacFilterThrottler.Functions.throttle_by_ip_path/1,
    scale: 60_000,
    limit: 50,
    exec_cond: &APIac.machine_to_machine?/1,
    error_response_verbosity: :debug}
end

Terminology

APIac uses the OAuth2 terminology:

• the client is the server, the machine, accessing the API

• the subject is the pysical user (real life person) on behalf on who the API access is performed. Note even though in most cases the subject has authenticated, but it should not be used as a proof of authentication since:

  • this may have be a long time ago (using OAuth2 refresh_token)

  • this may not be true at all:

    • in case the subject is impersonnated
    • when using UMA2 flows
  • OAuth2 is an access control protocol, not a federated authentication protocol

APIac plugs are designed for API accesses. Therefore, do not use it for end-user authentication as this may lead to security vulnerabilities. For example, the APIacAuthBasic authenticator does not handle weak user passwords and using it for browser-based authentication by end-user will result in security flaws.

Authenticators

The following table summarizes the information of the APIac authenticators:

Authenticator	Machine-to-machine	Accesses of subjects (real persons)
APIacAuthBasic	✔
APIacAuthBearer	OAuth2 client credentials flow	OAuth2 authorization code, implicit and password flows OpenID Connect flows
APIacAuthMTLS	✔
APIacAuthClientJWT	✔
APIacAuthClientSecretPost	✔

Machine-to-machine (also known as server-to-server or s2s) refers to access when only machines are involved, without subject.