xctx - Cross Context

Encrypted, signed, typed context propagation over a single HTTP header (X-Context) with Go and PHP reference implementations.

• Single header transport (v1.<base64url(JSON)>)
• AEAD (AES‑256‑GCM) with per‑message nonce, versioning, and key IDs (KID) for rotation
• Claims (iss, aud, iat, nbf, exp, jti) validated on the callee
• Typed payload T (Go generics) / associative array (PHP) — the library is schema‑agnostic
• AAD binding for tenant/env binding (non‑secret but must match on both sides)
• Cross‑language interop (Go ↔ PHP) proven in examples

License: Apache‑2.0 (see LICENSE-APACHE-2.0.txt). Composer package declares Apache-2.0.

Why

Passing many fields across services via body/query/headers is brittle and leaky (and sometimes plain-text). xctx gives you a single, encrypted, signed envelope carrying exactly the system-defined context you want — no more, no less — without the library knowing your field schema.

File Structure

xctx
├── LICENSE-APACHE-2.0.txt
├── README.md
├── clover.xml
├── composer.json
├── composer.lock
├── coverage.out
├── example
│   ├── callee
│   │   ├── go.mod
│   │   ├── main.go
│   │   └── main.php
│   └── caller
│       ├── go.mod
│       ├── main.go
│       └── main.php
├── go.mod
├── phpunit.xml.dist
├── src
│   └── Xctx
│       ├── Codec.php
│       ├── Config.php
│       ├── Exception
│       │   ├── CryptoException.php
│       │   ├── ValidationException.php
│       │   └── XctxException.php
│       ├── Keyring.php
│       └── Util
│           └── Base64Url.php
├── test
│   ├── CodecExceptionBranchesTest.php
│   ├── CodecTest.php
│   ├── ConfigTest.php
│   └── overrides
│       └── crypto_overrides.php
├── xctx.go
├── xctx_blackbox_test.go
├── xctx_config.go
├── xctx_config_blackbox_test.go
├── xctx_config_whitebox_test.go
└── xctx_whitebox_test.go

Quick Start

See USAGE.md for comprehensive instructions. TL;DR:

Go

type PassingContext struct {
    UserID   int32  `json:"user_id"`
    UserName string `json:"user_name"`
    Role     string `json:"role,omitempty"`
}

user := xctx.Config{ /* header, issuer, audience, TTL, keys... */ }
aad  := func() []byte { return []byte("TENANT=blue|ENV=dev") }

codec, typedKey, err := xctx.BuildCodecFromEnvWithKey[PassingContext](user, nil, aad)
if err != nil { /* handle */ }

// Caller: inject typed payload into context and seal
ctx := xctx.DefaultInjector[PassingContext](typedKey)(context.Background(), PassingContext{UserID:7, UserName:"arie"})
name, value, _ := codec.EmbedHeaderCtx(ctx) // ("X-Context", "v1.<...>")

// Callee: parse from *http.Request
newCtx, payload, err := codec.ParseCtx(r)

PHP

use ArieDeha\Xctx\{Config, Codec};

$user = new Config(headerName: 'X-Context', issuer: 'svc-caller', audience: 'svc-callee',
                   ttlSeconds: 120, currentKid: 'kid-demo',
                   currentKey: '0123456789abcdef0123456789abcdef');
$aad  = fn() => 'TENANT=blue|ENV=dev';

$codec = Codec::buildFromEnv($user, $aad);

// Caller: seal
[$name, $value] = $codec->embedHeader(['user_id'=>7,'user_name'=>'arie']);

// Callee: parse
[$payload, $claims] = $codec->parseHeaderValue($value);

Examples

• Go callee at :8081 and PHP callee at :8082 with mutual relays/mutations.
• Go and PHP callers demonstrate cross‑language portability and chained updates.

Run order:

# Terminal A
go run ./example/callee

# Terminal B
php -S 127.0.0.1:8082 -t example/callee example/callee/router.php  # or: php -S 127.0.0.1:8082 example/callee/main.php

# Terminal C
go run ./example/caller

# Terminal D
php example/caller/main.php

Envelope

X-Context: v1.<base64url(json)> where json has lowercase keys:

{ "v":1, "alg":"AES256-GCM", "kid":"kid-demo", "n":"...", "ct":"..." }

Both implementations accept AES256-GCM/AES-256-GCM and lowercase/uppercase keys on parse. Emit is canonicalized to lowercase keys for interop with Go.

Configuration

See USAGE.md for environment variables, key formats (raw/hex/base64), and AAD binding guidance.

Development

• See DEVELOPERS.md for building, testing, and coverage (Go & PHP).
• Security notes: short TTLs, rotation with OtherKeys, replay mitigation with jti, strict claim checks.