secrets/crates/secrets-mcp/src/auth.rs

use axum::{
    extract::{Request, State},
    http::StatusCode,
    middleware::Next,
    response::Response,
};
use sqlx::PgPool;
use uuid::Uuid;

use secrets_core::service::api_key::validate_api_key;

use crate::client_ip;

/// Injected into request extensions after Bearer token validation.
#[derive(Clone, Debug)]
pub struct AuthUser {
    pub user_id: Uuid,
}

/// Axum middleware that validates Bearer API keys for the /mcp route.
/// Passes all non-MCP paths through without authentication.
pub async fn bearer_auth_middleware(
    State(pool): State<PgPool>,
    req: Request,
    next: Next,
) -> Result<Response, StatusCode> {
    let path = req.uri().path();
    let method = req.method().as_str();
    let client_ip = client_ip::extract_client_ip(&req);

    // Only authenticate /mcp paths
    if !path.starts_with("/mcp") {
        return Ok(next.run(req).await);
    }

    // Allow OPTIONS (CORS preflight) through
    if req.method() == axum::http::Method::OPTIONS {
        return Ok(next.run(req).await);
    }

    let auth_header = req
        .headers()
        .get(axum::http::header::AUTHORIZATION)
        .and_then(|v| v.to_str().ok());

    let raw_key = match auth_header {
        Some(h) if h.starts_with("Bearer ") => h.trim_start_matches("Bearer ").trim(),
        Some(_) => {
            tracing::warn!(
                method,
                path,
                %client_ip,
                "invalid Authorization header format on /mcp (expected Bearer …)"
            );
            return Err(StatusCode::UNAUTHORIZED);
        }
        None => {
            tracing::warn!(
                method,
                path,
                %client_ip,
                "missing Authorization header on /mcp"
            );
            return Err(StatusCode::UNAUTHORIZED);
        }
    };

    match validate_api_key(&pool, raw_key).await {
        Ok(Some(user_id)) => {
            tracing::debug!(?user_id, "api key authenticated");
            let mut req = req;
            req.extensions_mut().insert(AuthUser { user_id });
            Ok(next.run(req).await)
        }
        Ok(None) => {
            tracing::warn!(
                method,
                path,
                %client_ip,
                key_prefix = %&raw_key.chars().take(12).collect::<String>(),
                key_len = raw_key.len(),
                "invalid api key (not found in database — e.g. revoked key or DB was reset; update MCP client Bearer token)"
            );
            Err(StatusCode::UNAUTHORIZED)
        }
        Err(e) => {
            tracing::error!(
                method,
                path,
                %client_ip,
                error = %e,
                "api key validation error"
            );
            Err(StatusCode::INTERNAL_SERVER_ERROR)
        }
    }
}