Document AZURE_TOKEN_CREDENTIALS breaking change in Aspire 13.0

[Copilot]

Aspire 13.0 now automatically sets AZURE_TOKEN_CREDENTIALS=managedidentity when deploying to Azure Container Apps or App Service, changing DefaultAzureCredential to use only ManagedIdentityCredential instead of the full credential chain.

Changes

• Breaking changes section (whats-new/aspire-13.mdx): Added "DefaultAzureCredential behavior in Azure deployments" documenting the environment variable, affected APIs (AddAzureContainerAppEnvironment, AddAzureAppServiceEnvironment), and migration paths for users needing the previous behavior

• Azure Container Apps docs (configure-container-apps.mdx): Added note callout explaining the automatic environment variable and linking to breaking change details

• Azure App Service docs (azure-app-service.mdx): Added note callout explaining the automatic environment variable and linking to breaking change details

Migration Example

Users requiring the previous credential chain behavior can remove the environment variable:

builder.AddProject<Projects.Frontend>("frontend")
    .PublishAsAzureContainerApp((infra, app) =>
    {
        var container = app.Template.Containers[0].Value!;
        var envVar = container.Env
            .Single(v => v.Value!.Name.Value == "AZURE_TOKEN_CREDENTIALS");
        container.Env.Remove(envVar);
    });

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[Copilot]

Pull request overview

This PR documents a breaking change in Aspire 13.0 where DefaultAzureCredential behavior changes when deploying to Azure Container Apps or App Service. The change ensures deterministic authentication by automatically setting AZURE_TOKEN_CREDENTIALS=managedidentity, forcing DefaultAzureCredential to use only ManagedIdentityCredential instead of attempting the full credential chain.

Changes:

• Added comprehensive breaking change documentation in the "What's new in Aspire 13" article explaining the AZURE_TOKEN_CREDENTIALS environment variable behavior
• Added note callouts in Azure Container Apps and Azure App Service documentation pages linking to the breaking change details
• Improved formatting/indentation consistency throughout the what's-new document

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/frontend/src/content/docs/whats-new/aspire-13.mdx	Added "DefaultAzureCredential behavior in Azure deployments" section under breaking changes with detailed explanation, affected APIs, and migration examples. Also includes formatting improvements.
src/frontend/src/content/docs/integrations/cloud/azure/configure-container-apps.mdx	Added note callout explaining the automatic AZURE_TOKEN_CREDENTIALS environment variable and linking to breaking change documentation.
src/frontend/src/content/docs/integrations/cloud/azure/azure-app-service.mdx	Added note callout explaining the automatic AZURE_TOKEN_CREDENTIALS environment variable and linking to breaking change documentation.

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