DefaultAzureCredentialFactory currently takes the value of the EnvironmentVariables.CredentialSelection and makes it lowecase in order to avoid casing issues.

string credentialSelection = EnvironmentVariables.CredentialSelection?.Trim().ToLower();

However, if current thread culture is Turkish, "AZURECLICREDENTIAL". ToLowerO is equal to "azureclıcredentıal" (notice dotless lowercase 'i'). This creates an invalid value for comparison against the known valid values.

The DefaultAzureCredentialFactory should handle case insensitivity such that other culture settings work without issue.

Repro:

using System.Globalization;
using Azure.Core;
using Azure.Identity;
 
Thread.CurrentThread.CurrentCulture = new CultureInfo("TR-tr");
Environment.SetEnvironmentVariable(DefaultAzureCredential.DefaultEnvironmentVariableName, "AZURECLICREDENTIAL");
DefaultAzureCredential credential = new DefaultAzureCredential(DefaultAzureCredential.DefaultEnvironmentVariableName);
AccessToken token = credential.GetToken(new TokenRequestContext(scopes: ["[https://vault.azure.net/.default"]));
Console.WriteLine($"Access token acquired. Token type: {token.TokenType}, ExpiresOn: {token.ExpiresOn}");