feat(csharp): add support for inferred authentication scheme

[devin-ai-integration]

feat(csharp): Add Inferred Authentication Support

Summary

This PR implements support for the inferred authentication scheme in the C# SDK generator. Inferred authentication is a pattern where authentication credentials are automatically obtained by calling a token endpoint (e.g., OAuth client credentials flow) before making authenticated API requests. The generator now:

• Generates an InferredAuthTokenProvider class that handles token acquisition and caching
• Automatically configures the root client to use inferred auth when specified in the API definition
• Implements token expiry tracking and automatic refresh with a configurable buffer
• Supports multiple authenticated headers from the token response
• Updates mock server tests to include inferred auth endpoint mocking

Key Changes

Generator Implementation

New Generator Component (InferredAuthTokenProviderGenerator.ts):

• Generates InferredAuthTokenProvider class in the Core namespace
• Extracts credential parameters from the token endpoint (headers and body properties)
• Implements GetAuthHeadersAsync() method with caching and expiry support
• Builds response property accessors for flexible token response structures
• Handles value prefixes (e.g., "Bearer ") for authentication headers

Root Client Integration (RootClientGenerator.ts):

• Instantiates InferredAuthTokenProvider with required credentials
• Configures client headers using lazy evaluation (Func<string>) to avoid blocking constructor calls
• Adds constructor parameters for inferred auth credentials
• Generates example values in snippets/documentation

Context Updates (SdkGeneratorContext.ts):

• Added getInferredAuth() helper method to detect inferred auth schemes

Generator Entry Point (SdkGeneratorCli.ts):

• Conditionally generates InferredAuthTokenProvider when inferred auth is detected

Generated Code Updates

Seed Test Fixtures (4 fixtures updated):

• inferred-auth-explicit - Explicit auth with client credentials
• inferred-auth-implicit-no-expiry - No expiry tracking
• inferred-auth-implicit - Implicit auth with expiry
• websocket-inferred-auth - WebSocket-specific inferred auth

Each fixture now includes:

• Generated InferredAuthTokenProvider class (example)
• Updated client initialization with credential parameters
• Mock server test support for token endpoints

Mock Server Test Integration

Base Mock Server Test Generator (BaseMockServerTestGenerator.ts):

• Added MockInferredAuthEndpoint method to mock token responses
• Configures WireMock to return appropriate auth tokens for tests
• Ensures tests can run without real authentication services

Technical Implementation Details

Token Caching Strategy

The generated provider implements efficient token management:

private IDictionary<string, string>? _cachedHeaders;
private DateTime? _expiresAt;

public async Task<IDictionary<string, string>> GetAuthHeadersAsync()
{
    if (_cachedHeaders == null || DateTime.UtcNow >= _expiresAt)
    {
        // Refresh token
    }
    return _cachedHeaders;
}

Lazy Header Evaluation

Headers use Func<string> to avoid blocking the client constructor:

clientOptions.Headers["Authorization"] = new Func<string>(() =>
    inferredAuthProvider.GetAuthHeadersAsync().Result["Authorization"]
);

Credential Parameter Collection

The generator intelligently extracts required credentials:

• Skips literal values (hardcoded in requests)
• Skips optional parameters for simplicity
• Collects both header and body parameters
• Uses PascalCase property names for request initialization

Testing

All seed test fixtures have been regenerated and validated:

• ✅ inferred-auth-explicit - Tests explicit client credentials flow
• ✅ inferred-auth-implicit - Tests implicit auth with token expiry
• ✅ inferred-auth-implicit-no-expiry - Tests auth without expiry tracking
• ✅ websocket-inferred-auth - Tests WebSocket-specific auth scenarios

Mock server tests ensure the generated code works correctly without external dependencies.

Files Changed

Generator Source (5 files)

• generators/csharp/codegen/src/context/generation-info.ts - Added InferredAuthTokenProvider type reference
• generators/csharp/sdk/src/SdkGeneratorCli.ts - Added generator instantiation
• generators/csharp/sdk/src/SdkGeneratorContext.ts - Added helper method
• generators/csharp/sdk/src/inferred-auth/InferredAuthTokenProviderGenerator.ts - New generator (337 lines)
• generators/csharp/sdk/src/root-client/RootClientGenerator.ts - Client integration (+264 lines)

Test Infrastructure (1 file)

• generators/csharp/sdk/src/test/mock-server/BaseMockServerTestGenerator.ts - Mock server support

Generated Seed Outputs (17 files)

• 4 InferredAuthTokenProvider implementations
• 4 updated client classes
• 4 updated mock server tests
• 4 updated READMEs
• 1 updated snippet.json file

Version Configuration (1 file)

• generators/csharp/sdk/versions.yml - Updated version metadata

Breaking Changes

None. This is an additive feature that only affects SDKs using the inferred authentication scheme.

Next Steps

• Monitor generated SDK usage in production
• Consider adding support for optional credential parameters
• Evaluate async/await improvements to avoid .Result blocking in header suppliers

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