[Bug] Threading exception when using ExtraQueryParameters

[bgavrilMS]

Library version used

4.66

.NET version

net8

Scenario

ConfidentialClient - service to service (AcquireTokenForClient), ConfidentialClient - web api (AcquireTokenOnBehalfOf), ConfidentialClient - web site (AcquireTokenByAuthCode)

Is this a new or an existing app?

The app is in production, and I have upgraded to a new version of MSAL

Issue description and reproduction steps

For details see AzureAD/microsoft-identity-web#3228

Note that Id.Web always sets extra QP when calling Downstream API.

It's very easy to repro in MSAL:

1. Create a CCA
2. Call AcquireTokenForClient from 5 threads in a loop

Relevant code snippets

Expected behavior

No response

Identity provider

Microsoft Entra ID (Work and School accounts and Personal Microsoft accounts)

Regression

No response

Solution and workarounds

No response

[bgavrilMS]

Marking as P1 as it repros quite easily with few threads.