Add basic documentation for LDAP & OAuth support

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

docs/administration/configure/auth.md

@@ -0,0 +1,113 @@
+# Authentification
+
+## LDAP
+
+Use LDAP for user authentication.  When a user logs in to the Mobilizon instance, the email and password will be verified by trying to authenticate
+(bind) to an LDAP server. If a user exists in the LDAP directory but there is no account with the same email yet on the Mobilizon instance then a new
+Mobilizon account will be created (without needing email confirmation) with the same email as the LDAP email name.
+
+!!! tip
+    As Mobilizon uses email for login and LDAP bind is often done with account UID/CN, we need to start by searching for LDAP account matching with this email. LDAP search without bind is often disallowed, so you'll probably need an admin LDAP user.
+
+
+Change authentification method:
+```elixir
+config :mobilizon,
+       Mobilizon.Service.Auth.Authenticator,
+       Mobilizon.Service.Auth.LDAPAuthenticator
+```
+
+LDAP configuration under `:mobilizon, :ldap`:
+
+* `enabled`: enables LDAP authentication
+* `host`: LDAP server hostname
+* `port`: LDAP port, e.g. 389 or 636
+* `ssl`: true to use SSL, usually implies the port 636
+* `sslopts`: additional SSL options
+* `tls`: true to start TLS, usually implies the port 389
+* `tlsopts`: additional TLS options
+* `base`: LDAP base, e.g. "dc=example,dc=com"
+* `uid`: LDAP attribute name to authenticate the user, e.g. when "cn", the filter will be "cn=username,base"
+* `require_bind_for_search` whether admin bind is required to perform search
+* `bind_uid` the admin uid/cn for binding before searching
+* `bind_password` the admin password for binding before searching
+
+Example:
+
+```elixir
+config :mobilizon, :ldap,
+  enabled: true,
+  host: "localhost",
+  port: 636,
+  ssl: true,
+  sslopts: [],
+  tls: true,
+  tlsopts: [],
+  base: "ou=users,dc=example,dc=local",
+  uid: "cn",
+  require_bind_for_search: true,
+  bind_uid: "admin_account",
+  bind_password: "some_admin_password"
+```
+
+## OAuth
+
+Mobilizon currently supports the following providers:
+
+* [Discord](https://github.com/schwarz/ueberauth_discord)
+* [Facebook](https://github.com/ueberauth/ueberauth_facebook)
+* [Github](https://github.com/ueberauth/ueberauth_github)
+* [Gitlab](https://github.com/mtchavez/ueberauth_gitlab) (including self-hosted)
+* [Google](https://github.com/ueberauth/ueberauth_google)
+* [Keycloak](https://github.com/Rukenshia/ueberauth_keycloak) (through OpenID Connect)
+* [Twitter](https://github.com/Rukenshia/ueberauth_keycloak)
+
+Support for [other providers](https://github.com/ueberauth/ueberauth/wiki/List-of-Strategies) can easily be added if requested.
+
+!!! tip
+    We advise to look at each provider's README file for eventual specific instructions.
+
+You'll have to start by registering an app at the provider. Be sure to activate features like "Sign-in with" and "emails" scope, as Mobilizon needs users emails to register them.
+
+Add the configured providers to configuration (you may find the appropriate scopes on the provider's API documentation):
+```elixir
+config :ueberauth,
+       Ueberauth,
+       providers: [
+         gitlab: {Ueberauth.Strategy.Gitlab, [default_scope: "read_user"]},
+         keycloak: {Ueberauth.Strategy.Keycloak, [default_scope: "email"]}
+         # ...
+       ]
+```
+
+In order for the « Sign-in with » buttons to be added on Register and Login pages, list your providers:
+```elixir
+config :mobilizon, :auth,
+  oauth_consumer_strategies: [
+    :gitlab,
+    {:keycloak, "My corporate account"}
+    # ...
+  ]
+```
+
+!!! note
+    If you use the `{:provider_id, "Some label"}` form, the label will be used inside the buttons on Register and Login pages.
+
+Finally add the configuration for each specific provider. The Client ID and Client Secret are at least required:
+```elixir
+config :ueberauth, Ueberauth.Strategy.Facebook.OAuth,
+  client_id: "some_numeric_id",
+  client_secret: "some_secret"
+
+keycloak_url = "https://some-keycloak-instance.org"
+
+# Realm may be something else than master
+config :ueberauth, Ueberauth.Strategy.Keycloak.OAuth,
+  client_id: "some_id",
+  client_secret: "some_hexadecimal_secret",
+  site: keycloak_url,
+  authorize_url: "#{keycloak_url}/auth/realms/master/protocol/openid-connect/auth",
+  token_url: "#{keycloak_url}/auth/realms/master/protocol/openid-connect/token",
+  userinfo_url: "#{keycloak_url}/auth/realms/master/protocol/openid-connect/userinfo",
+  token_method: :post
+```