I am using Next.js 14.2.1 with the AppRouter. I am experiencing an incredibly strange error, where, no matter what I do, I am getting a 401 unauthorized response.

The point of the route is to take the firebase session cookie, post it to this route, and then use the Firebase Admin SDK to verify that it's still valid. Below is the code for the route handler:

export async function POST(request: Request, response: Response) {
    const firebaseAuth: Auth = adminApp.auth();

    try {
        const payload: Payload = await request.json();
        const sessionCookie: string = payload.sessionCookie;

        if (!sessionCookie) {
            return Response.json({}, { status: 401, statusText: "Unauthorized" });
        }

        try {
            const idToken: DecodedIdToken = await firebaseAuth.verifySessionCookie(sessionCookie);
            const nowInSeconds: number = Date.now() / 1000;

            if (Object.entries(idToken).length > 0 && idToken.exp > nowInSeconds) {
                return Response.json({}, { status: 200, statusText: "Authorized" });
            }

            return Response.json(
                {},
                {
                    status: 401,
                    statusText: "Unauthorized",
                }
            );
        } catch (err: any) {
            console.error(new Error(err));
            return Response.json({ error: "Internal Server Error" }, { status: 500 });
        }
    } catch (err: any) {
        return Response.json({}, { status: 500, statusText: "Internal Server Error" });
    }
}

Originally, I was making the request to this route in middleware, because the edge runtime doesn't support the Firebase SDK. To rule out that this was causing a problem, I moved the call to a server component. Here is that call:

try {
        const validationResponse = await fetch("http://localhost:3000/api/validate", {
            method: "POST",
            headers: {
                "Content-Type": "application/json",
                "Access-Control-Allow-Methods": "GET, POST, PUT, DELETE, OPTIONS",
            },
            body: JSON.stringify({ sessionCookie: session.value }),
        });

        console.log("validate: ", validationResponse.status);
    } catch (err: any) {
        console.error(new Error(err));
    }

I have attached a screenshot of the folder structure where the route handler is defined, but based on the docs, I don't see how I could be defining it incorrectly.

I have tried making a request to the route using Postman, still it returns a 401.

Please, if you have any advice or feedback on why this is occurring, I could use the help.