Add an option to read SSO client secret from a file

src/core/config/check.rs

@@ -288,6 +288,35 @@ pub fn check(config: &Config) -> Result {
 		));
 	}
 
+	for (i, provider) in config.identity_provider.iter().enumerate() {
+		if provider.client_secret.is_some() {
+			continue;
+		}
+
+		let Some(secret_path) = &provider.client_secret_file else {
+			return Err!(Config(
+				"client_secret",
+				"Either client secret or a client secret file must be set on identity provider \
+				 №{i}."
+			));
+		};
+
+		let Ok(secret) = std::fs::read_to_string(secret_path) else {
+			return Err!(Config(
+				"client_secret_file",
+				"Client secret file was specified but failed to be read at identity provider \
+				 №{i}"
+			));
+		};
+
+		if secret.is_empty() {
+			return Err!(Config(
+				"client_secret_file",
+				"Client secret file was specified but is empty on identity provider №{i}"
+			));
+		}
+	}
+
 	Ok(())
 }
 

src/core/config/mod.rs

@@ -2517,7 +2517,15 @@ pub struct IdentityProvider {
 	/// Secret key the provider generated for you along with the `client_id`
 	/// above. Unlike the `client_id`, the `client_secret` can be changed here
 	/// whenever the provider regenerates one for you.
-	pub client_secret: String,
+	pub client_secret: Option<String>,
+
+	/// Secret key to use that's read from the file path specified.
+	///
+	/// This takes priority over "client_secret" first, and falls back to
+	/// "client_secret" if invalid or failed to open.
+	///
+	/// example: "/etc/tuwunel/.client_secret"
+	pub client_secret_file: Option<PathBuf>,
 
 	/// The callback URL configured when registering the OAuth application with
 	/// the provider. Tuwunel's callback URL must be strictly formatted exactly
@@ -2613,6 +2621,21 @@ pub struct IdentityProvider {
 impl IdentityProvider {
 	#[must_use]
 	pub fn id(&self) -> &str { self.client_id.as_str() }
+
+	pub async fn get_client_secret(&self) -> Result<String> {
+		if let Some(client_secret) = &self.client_secret {
+			return Ok(client_secret.clone());
+		}
+
+		futures::future::OptionFuture::from(
+			self.client_secret_file
+				.as_ref()
+				.map(tokio::fs::read_to_string),
+		)
+		.await
+		.transpose()?
+		.ok_or_else(|| err!("No client secret or client secret file configured"))
+	}
 }
 
 impl Hash for IdentityProvider {

src/service/oauth/mod.rs

@@ -97,9 +97,11 @@ pub async fn revoke_token(&self, (provider, session): (&Provider, &Session)) ->
 		client_secret: &'a str,
 	}
 
+	let client_secret = provider.get_client_secret().await?;
+
 	let query = RevokeQuery {
 		client_id: &provider.client_id,
-		client_secret: &provider.client_secret,
+		client_secret: &client_secret,
 	};
 
 	let url = provider
@@ -130,9 +132,11 @@ pub async fn request_token(
 		redirect_uri: Option<&'a str>,
 	}
 
+	let client_secret = provider.get_client_secret().await?;
+
 	let query = TokenQuery {
 		client_id: &provider.client_id,
-		client_secret: &provider.client_secret,
+		client_secret: &client_secret,
 		grant_type: "authorization_code",
 		code,
 		code_verifier: session.code_verifier.as_deref(),