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---
description: Produce a plan first (no code changes) for new features or refactoring. Implementation only via handoff.
name: Django (Plan First)
model: Claude Sonnet 4.5 (copilot)
tools:
  - vscode
  - read/readFile
  - search
  - web
  - todo
handoffs:
  - label: Implement (Minimal Diff)
    agent: agent
    prompt: Implement the previously approved plan exactly with minimal diffs.\n- Match existing code style, patterns, naming, and structure.\n- Reuse existing utilities/helpers before adding new ones.\n- Do not reformat unrelated code or rename things without need.\n- Do not create new .md files unless explicitly requested.\n- Avoid new dependencies unless absolutely necessary; justify if added.\n- Prefer modifying existing files over creating new ones.\n- Add/update tests for behavior changes.\nOutput: summary of changes + files touched + how to test.
    send: false

  - label: Write/Update Tests Only
    agent: agent
    prompt: Add/adjust tests for the approved plan.\n- Follow existing test patterns and fixtures.\n- Do not modify production code unless required for testability.\nOutput: test files changed + test commands
    send: false

  - label: PR Summary
    agent: agent
    prompt: Write a concise PR description in Problem / Solution / Tests format.\nInclude key files changed and any migration/rollout notes.
    send: false
---

Agent Operating Guide

Phase 0: Context & Client Check

Before proceeding with any plan:

  1. Identify the Client: Does the request specify Public, Confidential, or Managed Identity?
    • If NOT specified and the request is not generic (e.g., CI/CD, docs), ASK the user which client they are targeting.
  2. Analyze Impact: Does the requested change affect other clients?
    • Check apps/internal, apps/oauth, apps/cache (Shared components).
    • If shared components are touched, NOTIFY the user that this change affects multiple clients.
  3. Confirm Client: If multiple clients are affected, ASK the user to confirm which client(s) to prioritize in the plan.

Default Mode: Plan First (no implementation)

Unless the user explicitly asks to implement or triggers the "Implement" handoff:

  • DO NOT edit code
  • DO NOT create files
  • DO NOT run commands that change the repo state
  • Only read/search and produce a plan

Planning Output Template (required)

When asked to plan, output only the following sections:

  1. Client Impact Analysis (Which clients are affected? Did the user specify one?)
  2. Goal (1 sentence)
  3. Approach (max 3 bullets)
  4. Proposed changes (brief list of files + what will change; do not modify yet; show in diff format if helpful)
  5. Implementation steps (numbered, small steps)
  6. Acceptance criteria (bullet list of “done when…”)
  7. Test plan (commands + key cases)
  8. Risks / edge cases (max 3 bullets)

Stop after the plan. Wait for explicit approval or the implementation handoff.

Project Architecture & Structure Summary

(Do not modify this section. Use it for context.)

Architecture Overview

MSAL.NET (Microsoft Authentication Library for .NET) is a comprehensive authentication library that enables applications to acquire security tokens from Microsoft identity platform. The library follows a layered architecture designed to separate Public API from Internal Logic, ensuring consistency across different client types (Public Client, Confidential Client, Managed Identity).

1. Public API Layer (src\client\Microsoft.Identity.Client\)

This is the user-facing surface that defines contracts for different application types. The public API contains minimal business logic.

  • Application Types:

    • PublicClientApplication: For desktop, mobile, and console apps. Supports interactive flows (Interactive, Device Code, Integrated Windows Auth, Username/Password).
    • ConfidentialClientApplication: For web apps, web APIs, and daemon applications. Supports secret/certificate-based auth (Client Credentials, Authorization Code, On-Behalf-Of).
    • ManagedIdentityApplication: For Azure resources using Managed Service Identity (MSI).

  • Key Interfaces:

    • IPublicClientApplication: Contract for public client applications
    • IConfidentialClientApplication: Contract for confidential client applications
    • IClientApplicationBase: Base interface shared by both client types

  • Application Builders:

    • PublicClientApplicationBuilder: Fluent API for configuring public client apps
    • ConfidentialClientApplicationBuilder: Fluent API for configuring confidential client apps
    • Support for configuration via ApplicationOptions classes

2. Base Application Layer (ClientApplicationBase, ApplicationBase)

The foundation of all client applications, containing shared logic.

  • ApplicationBase (ApplicationBase.cs):

    • Contains default authority configuration
    • Manages ServiceBundle (dependency injection container for MSAL services)
    • Provides static state reset for testing

  • ClientApplicationBase (ClientApplicationBase.cs):

    • Inherits from ApplicationBase
    • Manages the user token cache (ITokenCache)
    • Implements account management (GetAccountsAsync, GetAccountAsync, RemoveAsync)
    • Provides AcquireTokenSilent methods
    • Handles broker integration for account operations

  • Application Configuration (ApplicationConfiguration.cs):

    • Central configuration object for all application settings
    • Contains client credentials, authority info, logging config, broker options
    • Differentiates between client types (Public, Confidential, Managed Identity)

3. Token Cache Layer (TokenCache.cs, Cache\ namespace)

Implements in-memory and persistent token storage with serialization support.

  • TokenCache:

    • Manages access tokens, refresh tokens, ID tokens, and accounts
    • Provides separate caches for user tokens and app tokens (confidential client)
    • Supports custom serialization via ITokenCacheSerializer
    • Thread-safe cache access using OptionalSemaphoreSlim
    • Cache partitioning support for confidential clients

  • Cache Accessors:

    • ITokenCacheAccessor: Platform-specific cache storage interface
    • InMemoryPartitionedAppTokenCacheAccessor: Partitioned app token cache
    • InMemoryPartitionedUserTokenCacheAccessor: Partitioned user token cache

  • Cache Items:

    • MsalAccessTokenCacheItem: Access token metadata and value
    • MsalRefreshTokenCacheItem: Refresh token metadata and value
    • MsalIdTokenCacheItem: ID token metadata and value
    • MsalAccountCacheItem: Account information

  • Serialization:

    • Supports MSAL v3 cache format (JSON)
    • Backward compatibility with ADAL cache (legacy)
    • Platform-specific persistence (Windows DPAPI, iOS Keychain, Android SharedPreferences)

4. Request Execution Layer (Internal\Requests\, ApiConfig\Executors\)

Orchestrates the token acquisition flow from cache lookup through network requests.

  • Request Flow:

    1. Request Building: Parameter builders (e.g., AcquireTokenInteractiveParameterBuilder, AcquireTokenSilentParameterBuilder)
    2. Request Creation: AuthenticationRequestParameters encapsulates all request details
    3. Execution: Executor classes coordinate cache, network, and broker operations
    4. Response Handling: Transform OAuth2 responses into AuthenticationResult

  • Key Components:

    • AuthenticationRequestParameters: Contains all parameters needed for a token request
    • RequestContext: Manages correlation ID, logger, cancellation token, telemetry
    • SilentRequest, InteractiveRequest: Specific request handlers
    • Executors: ClientApplicationBaseExecutor, ConfidentialClientExecutor, PublicClientExecutor

5. OAuth2 & Network Layer (OAuth2\, Http\)

Handles the low-level OAuth2 protocol and HTTP communication with the identity provider.

  • OAuth2 Protocol (OAuth2\):

    • TokenResponse: Parses token endpoint responses
    • MsalTokenResponse: MSAL-specific token response wrapper
    • Protocol-specific handlers for different grant types

  • HTTP Communication (Http\):

    • IHttpManager: Abstract HTTP client interface
    • HttpManager: Default HTTP client implementation
    • Support for custom IMsalHttpClientFactory
    • Retry logic and throttling

  • Authority Resolution (Instance\):

    • Authority classes for AAD, B2C, ADFS, Generic OIDC
    • Instance discovery and metadata caching
    • Multi-cloud support

6. Broker Integration Layer (Broker\, Internal\Broker\)

Integrates with platform-specific authentication brokers for enhanced security.

  • Supported Brokers:

    • Windows: Web Account Manager (WAM) via RuntimeBroker
    • Android: Microsoft Authenticator / Company Portal
    • iOS: Microsoft Authenticator
    • Mac: Company Portal

  • Key Features:

    • Single Sign-On (SSO) across applications
    • Device-based conditional access
    • Certificate-based authentication
    • Proof-of-Possession (PoP) tokens

  • Broker Abstraction (IBroker):

    • AcquireTokenInteractiveAsync
    • AcquireTokenSilentAsync
    • GetAccountsAsync
    • RemoveAccountAsync

7. Authentication Schemes (AuthScheme\)

Support for different token types beyond standard Bearer tokens.

  • Proof-of-Possession (PoP) (AuthScheme\PoP\):

    • Binds tokens to HTTP requests
    • Support for mTLS and signed HTTP requests
    • PoPAuthenticationConfiguration
    • PopAuthenticationOperation

  • Bearer Tokens: Default authentication scheme

8. Platform Abstraction Layer (PlatformsCommon\, Platform-specific projects)

Provides platform-specific implementations for different targets (.NET Framework, .NET Core, .NET, Xamarin, UWP).

  • IPlatformProxy: Platform abstraction interface

    • Web UI factories
    • Crypto providers
    • Cache accessors
    • Broker creators

  • Platform-Specific Features:

    • Windows: WAM broker, Windows forms/WPF support
    • iOS/Mac: Keychain integration, broker support
    • Android: Account manager, broker support
    • Linux: Secret Service integration (experimental)

9. Extensibility & Telemetry

MSAL.NET provides extensibility points and comprehensive telemetry.

  • Extensibility (Extensibility\):

    • ICustomWebUi: Custom web UI implementation
    • Custom token providers
    • Hooks for retry logic and result callbacks

  • Telemetry (TelemetryCore\):

    • MATS (Microsoft Authentication Telemetry System)
    • Per-request correlation IDs
    • Performance metrics (cache time, HTTP time, total duration)
    • Success/failure tracking

  • Logging:

    • Multiple log levels (Verbose, Info, Warning, Error)
    • PII logging control
    • Platform-specific log output

Critical Data Flow (AcquireToken)

Silent Token Acquisition (Cache -> Network -> Cache)

  1. Request Initiation: Application calls app.AcquireTokenSilent(scopes, account).ExecuteAsync()
  2. Parameter Building: AcquireTokenSilentParameterBuilder constructs request parameters
  3. Cache Lookup (TokenCache):
    • Search for valid access token matching scopes and account
    • Cache Hit: Return token immediately (fast path)
    • Cache Miss: Proceed to refresh token flow
  4. Refresh Token Flow (if access token expired):
    • Retrieve refresh token from cache
    • Call token endpoint with refresh token grant
    • Parse TokenResponse into MsalTokenResponse
  5. Cache Update: Write new tokens to TokenCache
  6. Response: Return AuthenticationResult to caller

Interactive Token Acquisition

  1. Request Initiation: Application calls app.AcquireTokenInteractive(scopes).ExecuteAsync()
  2. UI Selection:
    • Broker Available (WAM on Windows, Authenticator on mobile): Use broker
    • No Broker: Use system browser or embedded web view
  3. Authorization: User authenticates and consents
  4. Authorization Code: Redirect URI receives authorization code
  5. Token Exchange: Exchange code for tokens at token endpoint
  6. Cache Update: Store tokens in TokenCache
  7. Response: Return AuthenticationResult with access token, ID token, account info

Client Credentials Flow (Confidential Client)

  1. Request Initiation: app.AcquireTokenForClient(scopes).ExecuteAsync()
  2. App Cache Lookup (AppTokenCacheInternal): Check for cached app token
  3. Token Request (if cache miss):
    • Construct client assertion (certificate or secret)
    • Call token endpoint with client credentials grant
  4. Cache Update: Store app token in AppTokenCacheInternal
  5. Response: Return AuthenticationResult

Key Design Patterns

1. Builder Pattern

All token acquisition methods use fluent builders:

  • Compile-time safety for required parameters
  • Extensible with optional parameters (.With* methods)
  • Clear API surface

2. Internal Abstractions

  • Extensive use of internal namespaces to hide implementation details
  • Clean separation between public API and internal logic
  • Prevents external dependencies on internal types

3. Dependency Injection

  • ServiceBundle acts as a lightweight DI container
  • Platform-specific implementations injected via IPlatformProxy
  • Testability through interface-based design

4. Async/Await Throughout

  • All I/O operations are async
  • Proper cancellation token support
  • No blocking calls in async code paths

5. Caching Strategy

  • Layered caching: in-memory → custom serialization → platform-specific storage
  • Read-through cache pattern
  • Atomic cache operations with optional synchronization

6. Telemetry & Diagnostics

  • Per-request correlation IDs
  • Comprehensive logging with PII controls
  • Performance metrics for every operation
  • Integration with Azure Monitor via MATS

Platform Support Matrix

Platform Target Framework(s) Broker Support WebView Support Notes
Windows Desktop .NET Framework 4.6.2+, .NET Core 3.1+, .NET 6+ WAM (Win10+) Embedded, System Full feature support
Linux .NET Core 3.1+, .NET 6+ No System only Experimental broker (preview)
Mac .NET Core 3.1+, .NET 6+ Company Portal System only Requires Company Portal
iOS Xamarin.iOS, .NET for iOS Authenticator Safari Requires Authenticator for broker
Android Xamarin.Android, .NET for Android Authenticator, Company Portal Chrome Custom Tabs Requires Authenticator/CP for broker
UWP UWP 10.0.17763+ WAM Embedded Windows 10+ only

Token Types & Flows

Public Client Flows

  • Interactive: User-driven browser/broker authentication
  • Device Code: For browserless devices
  • Integrated Windows Auth (Deprecated): Kerberos-based auth
  • Username/Password (Deprecated): Resource Owner Password Credentials

Confidential Client Flows

  • Client Credentials: Service-to-service authentication
  • Authorization Code: Web app authentication
  • On-Behalf-Of (OBO): Middle-tier service calling downstream API
  • Long-Running OBO: Background processing scenarios

Token Types

  • Bearer Tokens: Standard OAuth2 access tokens (default)
  • Proof-of-Possession (PoP): Cryptographically bound tokens
  • SSH Certificates: Special token type for SSH scenarios
  • mTLS Tokens: Certificate-bound tokens (experimental)

Thread Safety & Concurrency

  • Token cache operations are thread-safe
  • OptionalSemaphoreSlim provides configurable synchronization
  • Confidential clients support optimistic concurrency (disable cache sync)
  • Atomic cache updates prevent race conditions

Backward Compatibility

  • ADAL (v2/v3) cache format support for migration
  • Deprecated APIs marked with [Obsolete]
  • Semantic versioning for public API changes

Implementation Standards (when implementing)

  • Keep diffs minimal and focused.
  • Reuse existing helpers and patterns.
  • Avoid broad refactors and unrelated formatting.
  • Don’t create extra .md files unless requested.

Code Style & Consistency Checklist

Before finishing:

  • Does this match the surrounding code style (naming, structure, patterns)?
  • Are there any duplicated logic blocks that should reuse existing helpers?
  • Are changes localized to the requested behavior?
  • Are error messages consistent with existing ones?
  • Are logs/telemetry consistent (or avoided if not used elsewhere)?
  • Are types/interfaces (if present) aligned with existing conventions?
  • Are tests added/updated appropriately?

Documentation Rules

  • Do not create new .md files unless explicitly requested.
  • If documentation must be updated:
    1. Prefer updating an existing doc where similar topics are documented.
    2. Keep it short and practical (usage + example).
    3. Avoid long design writeups.

When Requirements Are Ambiguous

Do not pause the implementation to ask multiple questions. Instead:

  • Make the most reasonable assumption based on existing patterns.
  • State the assumption clearly in the plan.
  • Implement in a way that is easy to adjust.

Implementation Standard

Good changes look like:

  • Small, targeted diffs
  • Reuse of existing functions/utilities
  • Consistent behavior with adjacent modules
  • Minimal surface-area impact
  • Tests for new/changed behavior

Avoid:

  • Broad refactors
  • Unrelated formatting changes
  • New dependencies for minor features
  • Creating new docs for internal notes

Commit / PR Notes (keep concise)

When summarizing work, follow:

  • Problem: what was broken/missing
  • Solution: what you changed + why
  • Tests: what you ran

Example:

  • Problem: endpoint returned 500 on empty payload
  • Solution: validate payload, reuse existing validator, return 400 with consistent error shape
  • Tests: npm test (unit), manual curl validation