fix: validate username at get-identity (#5884)

Fix for #5867 (prevent undefined username)

Co-authored-by: nlf <nlf@github.com>

lib/utils/get-identity.js

@@ -12,7 +12,9 @@ module.exports = async (npm, opts) => {
   // No username, but we have other credentials; fetch the username from registry
   if (creds.token || creds.certfile && creds.keyfile) {
     const registryData = await npmFetch.json('/-/whoami', { ...opts })
-    return registryData.username
+    if (typeof registryData?.username === 'string') {
+      return registryData.username
+    }
   }
 
   // At this point, even if they have a credentials object, it doesn't have a

test/lib/commands/whoami.js

@@ -1,6 +1,7 @@
 const t = require('tap')
 const { load: loadMockNpm } = require('../../fixtures/mock-npm')
 const MockRegistry = require('@npmcli/mock-registry')
+const nock = require('nock')
 
 const username = 'foo'
 const auth = { '//registry.npmjs.org/:_authToken': 'test-auth-token' }
@@ -67,3 +68,27 @@ t.test('not logged in', async t => {
   })
   await t.rejects(npm.exec('whoami', []), { code: 'ENEEDAUTH' })
 })
+
+t.test('non-string username in response', async t => {
+  nock.disableNetConnect()
+  t.teardown(() => {
+    nock.enableNetConnect()
+  })
+
+  const server = nock('https://registry.npmjs.org', {
+    reqheaders: {
+      authorization: 'Bearer abcd1234',
+    },
+  })
+    .get('/-/whoami')
+    .reply(200, { username: null })
+
+  const { npm } = await loadMockNpm(t, {
+    config: {
+      '//registry.npmjs.org/:_authToken': 'abcd1234',
+    },
+  })
+
+  await t.rejects(npm.exec('whoami', []), { code: 'ENEEDAUTH' })
+  t.ok(server.isDone())
+})