> **Can't find what you're looking for?** Use `search_docs` on the docs MCP server at `https://mpp.dev/api/mcp` to find what you need.

# Core Types \[Challenge, Credential, and Receipt primitives]

These types map directly to HTTP headers—`WWW-Authenticate`, `Authorization`, and `Payment-Receipt`—and can be used independently of the higher-level client and server APIs.

```ruby
require "mpp-rb"
```

## Parse a Challenge

Parse a `WWW-Authenticate` header into a typed `Challenge`:

```ruby
challenge = Mpp::Challenge.from_www_authenticate(
  'Payment id="...", realm="...", method="tempo", intent="charge", request="eyJ..."'
)

challenge.method  # => "tempo"
challenge.intent  # => "charge"
```

## Create and serialize a Credential

Build a `Credential` and serialize it to an `Authorization` header:

```ruby
credential = Mpp::Credential.new(
  id: "challenge-id",
  payload: { "type" => "transaction", "signature" => "0x..." },
  source: "did:pkh:eip155:42431:0xa726a1...",
)

header = credential.to_authorization
# header = "Payment eyJ..."
```

## Parse and serialize a Receipt

Parse the `Payment-Receipt` response header:

```ruby
receipt = Mpp::Receipt.from_payment_receipt(header_value)
header = receipt.to_payment_receipt
```

## Type reference

| Type | Description |
|------|-------------|
| `Mpp::Challenge` | Server Challenge parsed from `WWW-Authenticate` |
| `Mpp::ChallengeEcho` | Echoed Challenge fields in a Credential |
| `Mpp::Credential` | Client Credential for the `Authorization` header |
| `Mpp::Receipt` | Server Receipt parsed from `Payment-Receipt` |