Disallow issuing temp credential with another temp credential. (#111)

We should not allow users to "wrap" a temporary credential with another
temporary credential. This is fine from a security standpoint because
such a credential will fail later while fetching API secrets. However,
allowing this is a confusing and perhaps hard to debug behavior, so we
prefer to fail fast.

packages/proxy/utils/tempCredentials.test.ts

@@ -4,6 +4,7 @@ import {
   makeTempCredentialsJwt,
   verifyTempCredentials,
   verifyJwtOnly,
+  makeTempCredentials,
 } from "./tempCredentials";
 import {
   sign as jwtSign,
@@ -118,6 +119,26 @@ test("makeTempCredentialsJwt no secret reuse", () => {
   expect(payload1.jti).not.toStrictEqual(payload2.jti);
 });
 
+test("makeTempCredentials no wrapping other temp credential", async () => {
+  const result = makeTempCredentialsJwt({
+    request: { model: "model", ttl_seconds: 100 },
+    authToken: "auth token",
+    orgName: "my org name",
+  });
+
+  // Use the previous temp credential JWT to issue another one.
+  await expect(
+    makeTempCredentials({
+      authToken: result.jwt,
+      body: {
+        model: null,
+        ttl_seconds: 200,
+      },
+      cachePut: async () => undefined,
+    }),
+  ).rejects.toThrow();
+});
+
 test("verifyJwtOnly basic", () => {
   const credentialCacheValue: TempCredentialsCacheValue = {
     authToken: "auth token",

packages/proxy/utils/tempCredentials.ts

@@ -128,6 +128,16 @@ export async function makeTempCredentials({
     ttl_seconds?: number,
   ) => Promise<void>;
 }) {
+  if (isTempCredential(authToken)) {
+    // Disallow issuing a temp credential that wraps another temp credential.
+    // This is fine from a security standpoint because such a credential will
+    // fail later while fetching API secrets. However, allowing this is a
+    // confusing and perhaps hard to debug behavior, so we prefer to fail fast.
+    throw new Error(
+      "Temporary credential cannot be used to issue another temp credential.",
+    );
+  }
+
   const body = credentialsRequestSchema.safeParse(rawBody);
   if (!body.success) {
     throw new Error(body.error.message);