ApplicationInsights:Could not decode the auth cookie with error

[DevRCRun]

SDK Version: 2.9.6
Express version: 4.21.1

The above version of the SDK is in use with an Express application, installed on Windows Server.

ApplicationInsights:Could not decode the auth cookie with error: [
"[object Error]{ stack: 'URIError: URI malformed\n" +
' at decodeURI ()\n' +
' at HttpRequestParser._getId (\node_modules\applicationinsights\out\AutoCollection\HttpRequestParser.js:217:26)\n' +
' at HttpRequestParser.getRequestTags (\node_modules\applicationinsights\out\AutoCollection\HttpRequestParser.js:118:110)\n' +
' at AutoCollectHttpRequests.endRequest (\node_modules\applicationinsights\out\AutoCollection\HttpRequests.js:232:55)\n' +
' at ServerResponse. (\node_modules\applicationinsights\out\AutoCollection\HttpRequests.js:192:41)\n' +
' at Object.onceWrapper (node:events:631:28)\n' +
' at ServerResponse.clsBind (\node_modules\cls-hooked\context.js:172:17)\n' +
' at ServerResponse.emit (node:events:529:35)\n' +
' at ServerResponse.emitted (\node_modules\emitter-listener\listener.js:134:21)\n' +
" at onFinish (node:_http_outgoing:1008:10)', message: 'URI malformed', name: 'URIError'"
]

Could you advise / provide some context as to why this might occur? the Module is being loaded relatively simply using the application insights connection string

const appInsights = require('applicationinsights')
appInsights
.setup()
appInsights.defaultClient.context.tags[appInsights.defaultClient.context.keys.cloudRole] = 'our-name'
appInsights.start()

I wouldn't be surprised if a malformed request had caused the error (most day to day requests are not causing the error), however I don't understand what the auth cookie aspect refers to.

Many thanks

[JacksonWeber]

@DevRCRun We try to parse some values from cookies in the HttpRequestParser. This warning comes from a function concerned with parsing the ai_authUser from the request's cookies. We run decodeURI() on the cookie when trying to get this value. If that function throws an error we catch and log the warning you're seeing above. As the exception is handled and just a warning is logged, this shouldn't impact export of request telemetry.

What format is your authUser cookie in?