feat: Add native gRPC integration support

[developerkunal]

Description

This PR adds native gRPC support to the JWT middleware SDK, providing out-of-the-box integration for both unary and streaming gRPC methods.

Changes

• Added gRPC interceptors for unary and streaming methods in integrations/grpc/
• Implemented metadata-based token extraction following gRPC conventions
• Added comprehensive test coverage including unit and integration tests
• Created working example with proto definitions and server implementation
• Updated main README with gRPC usage documentation
• Added detailed integration README with examples and API reference

Usage Example

import (
    "google.golang.org/grpc"
    "github.com/auth0/go-jwt-middleware/v3/validator"
    jwtgrpc "github.com/auth0/go-jwt-middleware/v3/integrations/grpc"
)

// Create validator
jwtValidator, err := validator.New(
    keyFunc,
    validator.HS256,
    "https://your-issuer.com/",
    []string{"your-audience"},
)

// Create gRPC interceptor
interceptor, err := jwtgrpc.New(
    jwtgrpc.WithValidator(jwtValidator),
    jwtgrpc.WithExcludedMethods("/grpc.health.v1.Health/Check"),
)

// Create gRPC server with interceptors
grpcServer := grpc.NewServer(
    grpc.UnaryInterceptor(interceptor.UnaryServerInterceptor()),
    grpc.StreamInterceptor(interceptor.StreamServerInterceptor()),
)

// In your handlers, access claims:
func (s *server) GetUser(ctx context.Context, req *pb.GetUserRequest) (*pb.User, error) {
    claims, err := jwtgrpc.GetValidatedClaims(ctx)
    if err != nil {
        return nil, status.Error(codes.Unauthenticated, "invalid token")
    }
    
    // Use claims...
    userID := claims.RegisteredClaims.Subject
    return &pb.User{Id: userID}, nil
}

References

#181

Testing

• Unit tests pass
• Integration tests pass
• Example server runs successfully
• Test coverage maintained

[codecov-commenter]

Codecov Report

❌ Patch coverage is 96.09756% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.49%. Comparing base (3b2a7f3) to head (2370a44).

Files with missing lines	Patch %	Lines
integrations/grpc/interceptor.go	95.87%	2 Missing and 2 partials ⚠️
integrations/grpc/option.go	89.74%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #377      +/-   ##
==========================================
- Coverage   96.55%   96.49%   -0.06%     
==========================================
  Files          18       23       +5     
  Lines        1508     1713     +205     
==========================================
+ Hits         1456     1653     +197     
- Misses         34       39       +5     
- Partials       18       21       +3     

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[Copilot]

Pull request overview

This PR adds comprehensive native gRPC support to the JWT middleware SDK, enabling seamless JWT authentication for gRPC services through interceptors for both unary and streaming methods.

Changes:

• Introduced gRPC-specific interceptors in integrations/grpc/ package with metadata-based token extraction
• Implemented comprehensive error mapping from JWT validation errors to appropriate gRPC status codes
• Added complete test coverage including unit tests, integration tests, and a fully functional example application

Reviewed changes

Copilot reviewed 19 out of 21 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
integrations/grpc/interceptor.go	Core JWT interceptor implementation for unary and streaming gRPC methods
integrations/grpc/option.go	Configuration options with builder pattern for interceptor setup
integrations/grpc/extractor.go	Token extraction from gRPC metadata following Bearer token conventions
integrations/grpc/error_handler.go	Maps JWT validation errors to appropriate gRPC status codes
integrations/grpc/claims.go	Type-safe claims retrieval helpers using generics
integrations/grpc/doc.go	Comprehensive package documentation with usage examples
integrations/grpc/*_test.go	Extensive unit tests for all components
examples/grpc-example/	Complete working example with server, client, and integration tests
examples/grpc-example/proto/	Protocol Buffer definitions and generated code
go.mod, go.sum	Added gRPC dependencies (v1.78.0)
README.md	Updated main documentation with gRPC usage examples

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