# PlugHmac

**Auth Plug**

## Installation

The package can be installed by adding `plug_hmac` to your list of dependencies in `mix.exs`:

```elixir
def deps do
  [
    {:plug_hmac, "~> 0.3"}
  ]
end
```

## Usage

### Configuration

Add `body_reader` to your Phoenix's `Endpoint`
```elixir
plug Plug.Parsers,
    parsers: [:urlencoded, :multipart, :json],
    pass: ["*/*"],
    body_reader: {PlugHmac.CacheBodyReader, :read_body, []},
    json_decoder: Phoenix.json_library()
```

Setting `client_id` & `secrets`
```elixir
config :plug_hmac,
  secrets: %{
    "test_id" => "/dXOQgl57dXHT5LxHgtjXrxcbgGrUODvVZjcC8h4iFhTLGVTlwZw0W+vsA2lCOK8"
  }
```


### For Backend

```elixir
plug PlugHmac, auth_handler: __MODULE__
# or
plug PlugHmac, auth_handler: fun/2

# if set module must def the auth_error/2 function
def auth_error(conn, _error) do
  # you can case error here 
  # or update conn here
  # must return conn
  conn
end
```

### For Client
```elixir
PlugHmac.make_header("test_id", "GET", "/api/test_auth", "a1=123&a2=456", "body string")
"hmac id=test_id,signature=xpSI4lZe5c%2BxlNe%2BUK6MQU8RHZNTjL1CTgQLbFamoYU%3D,nonce=vrlaY%2BzdC2S7cdWEXLiN"
```

## Principle

客户端在请求时，需要在`HTTP`的`Header`增加`Authorization`:

```
Authorization: hmac id=test_id,signature=xpSI4lZe5c%2BxlNe%2BUK6MQU8RHZNTjL1CTgQLbFamoYU%3D,nonce=vrlaY%2BzdC2S7cdWEXLiN
```

`PlugHmac` `plug`会校验`Authorization`值的有效性

### 参数说明

在开始之前先说明将要用到的参数：

| 参数名      | 参数值               | 说明                         |
| ----------- | -------------------- | ---------------------------- |
| Method      | GET                  | 请求方法(全大写)             |
| Path        | /api/test_auth       | 请求路径                     |
| QueryString | "a1=123&a2=456"      | 将请求参数用`&`和`=`拼接起来 |
| Body        | "body string"        | 请求的body字符串             |
| ClientID    | test_id              | 由接口提供方提供             |
| SecretKey   | qhN8mkCzaxjC1jWD4fDW | 由接口提供方提供             |
| Nonce       | asd123               | 随机值字符串                 |



### 1. Authorization值

在拼接之前先使用 `URI-encode`，分别对各个参数值进行`encode`，然后再将其拼接起来，如下：

```
"hmac " + "id=" + ClientID + ",signature=" + Signature + ",nonce=" + Nonce
```

### 2. Signature值

首先按如下顺序拼接各个参数值：

```
ConcatString = Method+Path+QueryString+Body+Nonce
GET/api/test_autha1=123&a2=456body stringasd123
```

采用`HMAC_SHA256`算法使用`SecretKey`加密`ConcatString`的值，然后在进行`Base64-encode`，得到`Signature` 值，求值公式如下:

```
hmac.new(SecretKey, ConcatString, hashlib.sha256).digest().encode('base64')
Nop1kEtdf04S8Rr5U409Jmsx8Ic6zeWx2/HJZnLDRuM=
```