honoでhono/clientを利用したRPCモードでのクライアント通信を実装していたところ、CORS対応にて調べた内容。 hono: CORS設定 https://hono.dev/docs/middleware/builtin/cors app.use( "*", cors({ origin: "http://localhost:3000", allowHeaders: [ "X-Custom-Header", "Upgrade-Insecure-Requests", "Content-Type", "Authorization", ], allowMethods: ["POST", "GET", "OPTIONS"], maxAge: 600, credentials: true, }), ); その場合のclientではinit: {}にてcredentials設定を行う。 const _client = hc<ApiType>("http://localhost:5001", { headers: { "Content-Type": "application/json", }, init: { credentials: "include", }, }); https://github.com/orgs/honojs/discussions/2291