impl MSC2965: self-advertise as OIDC authentication provider

MSC2965 proposes to let the homeserver advertise its current OIDC authentication
issuer. These changes let conduwuit advertise itself as the issuer when
[global.auth.enable_oidc_login] is set. It also advertises its account management
endpoint if [global.auth.enable_oidc_account_management] is set.

None of these endpoints are implemented. This commit only implements the bare
advertisement, as requested by the MSC.

src/core/config/check.rs

@@ -289,6 +289,17 @@ pub fn check(config: &Config) -> Result {
 		));
 	}
 
+	if let Some(auth) = &config.auth {
+		if auth.enable_oidc_login {
+			if config.well_known.client.is_none() {
+				return Err!(Config(
+					"auth.enable_oidc_login",
+					"Oidc authentication is enabled but the well-known client is not set."
+				))
+			}
+		}
+	}
+
 	Ok(())
 }
 

src/core/config/mod.rs

@@ -104,7 +104,9 @@ pub struct Config {
 	#[serde(default)]
 	pub tls: TlsConfig,
 
-	/// The UNIX socket continuwuity will listen on.
+	pub auth: Option<AuthConfig>,
+
+	/// The UNIX socket conduwuit will listen on.
 	///
 	/// continuwuity cannot listen on both an IP address and a UNIX socket. If
 	/// listening on a UNIX socket, you MUST remove/comment the `address` key.
@@ -2020,6 +2022,20 @@ pub struct TlsConfig {
 	pub dual_protocol: bool,
 }
 
+#[derive(Clone, Debug, Deserialize, Default)]
+#[config_example_generator(filename = "conduwuit-example.toml", section = "global.auth")]
+pub struct AuthConfig {
+	/// Use this homeserver as the OIDC authentication reference.
+	/// Note that the legacy Matrix authentication still will work.
+	/// Unset by default.
+	pub enable_oidc_login: bool,
+
+	/// The URL where the user is able to access the account management
+	/// capabilities of the homeserver. Only used if `enable_oidc_login` is set.
+	/// Unset by default.
+	pub enable_oidc_account_management: bool,
+}
+
 #[allow(rustdoc::broken_intra_doc_links, rustdoc::bare_urls)]
 #[derive(Clone, Debug, Deserialize, Default)]
 #[config_example_generator(filename = "conduwuit-example.toml", section = "global.well_known")]