Issue #44: implement Rust client session values errors and CLI

clients/rust/src/auth.rs

@@ -1,5 +1,9 @@
 use std::fmt;
 
+use tonic::metadata::MetadataValue;
+use tonic::service::Interceptor;
+use tonic::{Request, Status};
+
 /// API key wrapper that avoids exposing raw credentials in formatted output.
 #[derive(Clone, Eq, PartialEq)]
 pub struct ApiKey(String);
@@ -28,3 +32,56 @@ impl fmt::Display for ApiKey {
         formatter.write_str("<redacted>")
     }
 }
+
+/// `tonic` interceptor that attaches gateway API key metadata.
+#[derive(Clone, Debug, Default)]
+pub struct AuthInterceptor {
+    api_key: Option<ApiKey>,
+}
+
+impl AuthInterceptor {
+    pub fn new(api_key: Option<ApiKey>) -> Self {
+        Self { api_key }
+    }
+}
+
+impl Interceptor for AuthInterceptor {
+    fn call(&mut self, mut request: Request<()>) -> Result<Request<()>, Status> {
+        if let Some(api_key) = &self.api_key {
+            let header_value = format!("Bearer {}", api_key.expose_secret())
+                .parse::<MetadataValue<_>>()
+                .map_err(|_| Status::unauthenticated("invalid API key metadata"))?;
+            request.metadata_mut().insert("authorization", header_value);
+        }
+
+        Ok(request)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use tonic::service::Interceptor;
+    use tonic::Request;
+
+    use super::{ApiKey, AuthInterceptor};
+
+    #[test]
+    fn api_key_debug_is_redacted() {
+        let key = ApiKey::new("mxgw_visible_secret");
+
+        assert_eq!(format!("{key:?}"), "ApiKey(\"<redacted>\")");
+        assert!(!format!("{key:?}").contains("visible_secret"));
+        assert_eq!(key.to_string(), "<redacted>");
+    }
+
+    #[test]
+    fn interceptor_attaches_bearer_metadata() {
+        let mut interceptor = AuthInterceptor::new(Some(ApiKey::new("mxgw_fixture_secret")));
+        let request = interceptor.call(Request::new(())).unwrap();
+
+        assert_eq!(
+            request.metadata().get("authorization").unwrap(),
+            "Bearer mxgw_fixture_secret"
+        );
+    }
+}