# SignedPolicy

## Overview

SignedPolicy is a module that limits the user's privileges and time. For example, operators can distribute RTMP URLs that can be accessed for 60 seconds to authorized users, and limit RTMP transmission to 1 hour. The provided URL will be destroyed after 60 seconds, and transmission will automatically stop after 1 hour. Users who are provided with a SignedPolicy URL cannot access resources other than the provided URL. This is because the SignedPolicy URL is authenticated.

SignedPolicy URL consists of the query string of the streaming URL with Policy and Signature as shown below. If SignedPolicy is enabled in the configuration of OvenMediaEngine, access to URLs with no signature or invalid signature is not allowed. Signature uses HMAC-SHA1 to authenticate all URLs except signature.

```
scheme://domain.com:port/app/stream?policy=<>&signature=<>
```

### Policy

Policy is in JSON format and provides the following properties.

```
{
    "url_activate":1399711581,                                    
    "url_expire":1399721581,                                    
    "stream_expire":1399821581,                                    
    "allow_ip":"192.168.100.5/32",
    "real_ip":"111.111.111.111/32"
}
```

<table><thead><tr><th width="156.33333333333331">Key</th><th width="162">Value</th><th>Description</th></tr></thead><tbody><tr><td><p>url_expire</p><p><strong>(Required)</strong></p></td><td>&#x3C;Number> Milliseconds since unix epoch</td><td><strong>The time the URL expires</strong><br>Reject on request after the expiration</td></tr><tr><td><p>url_activate</p><p><strong>(Optional)</strong></p></td><td>&#x3C;Number> Milliseconds since unix epoch</td><td><strong>The time the URL activates</strong><br>Reject on request before activation</td></tr><tr><td><p>stream_expire</p><p><strong>(Optional)</strong></p></td><td>&#x3C;Number> Milliseconds since unix epoch</td><td><strong>The time the Stream expires</strong><br>Transmission and playback stop when the time expires</td></tr><tr><td><p>allow_ip</p><p><strong>(Optional)</strong></p></td><td>&#x3C;String> IPv4 CIDR</td><td><p><strong>Allowed IP Address Range</strong></p><p>Check the IP address of the client connected to the server</p></td></tr><tr><td>real_ip<br><strong>(Optional)</strong></td><td>&#x3C;String> IPv4 CIDR</td><td><p><strong>Allowed IP Address Range</strong></p><p>Check the IP address of the client forwarded by the proxy server</p></td></tr></tbody></table>

{% hint style="info" %}
**url\_expire** means the time the URL is valid, so if you connect before the URL expires, you can continue to use it, and sessions that have already been connected will not be deleted even if the time expires. However, **stream\_expire** forcibly terminates the session when the time expires even if it is already playing.
{% endhint %}

{% hint style="info" %}
If `real_ip` is in the policy, OME searches for and checks the values ​​in the following order.

1. The value of the **X-REAL-IP** header
2. The value of the first item of **X-FORWARDED-FOR**
3. The IP of the client that actually connected
   {% endhint %}

### Signature

Signature is generated by HMAC-SHA1 encoding all URLs except signature query string. The generated Signature is encoded using [Base64URL](https://tools.ietf.org/html/rfc4648#section-5) and included as a query string of the existing URL.

```
Base64URL.Encode(
    HMAC.Encrypt(
        SHA1, 
        secret_key, 
        "scheme://domain.com:port/app/stream[/file]?policy='encoded policy'>"
    )
)
```

{% hint style="danger" %}
The URL entered into HMAC to generate the Signature must include :port.

When creating a signature, you cannot omit the default port such as http port 80, https port 443, or rtmp port 1935. This is because when OvenMediaEngine creates a signature for checking the signature, it is created by putting the port value.

This also applies when using a domain name instead of an IP address. For example:

* `wss://stream.example.com:3334/app/stream` (correct)
* `wss://stream.example.com/app/stream` (incorrect — signature will not match)
  {% endhint %}

{% hint style="danger" %}
When using SignedPolicy with [SRT providers](https://ovenmediaengine-enterprise.gitbook.io/guide/features/access-control-and-security/broken-reference), only use the **streamid** portion of the URL, e.g. srt://myserver:9999?streamid=**srt://myserver:9999/app/stream?policy=abc123**
{% endhint %}

{% hint style="danger" %}
When using SignedPolicy with [SRT publishers](https://ovenmediaengine-enterprise.gitbook.io/guide/features/access-control-and-security/broken-reference), you must generate the SignedPolicy using the `streamid`.

For example, to generate a SignedPolicy for the URL `srt://1.2.3.4:9998?streamid=default/app/stream`, you can use the following command:

```bash
$ ./simple_signed_policy_url_generator.sh ome_is_the_best \
    srt://default/app/stream signature policy 600
[URL] srt://default/app/stream?policy=__POLICY__&signature=__SIGNATURE__
[Percent encoded URL] srt%3A//default/app/stream%3Fpolicy%3D__POLICY__%26signature%3D__SIGNATURE__
```

When the SignedPolicy is applied, the final SRT URL becomes `srt://1.2.3.4:9998?streamid=default%2Fapp%2Fstream%3Fpolicy%3D__POLICY__%26signature%3D__SIGNATURE__`.
{% endhint %}

## Configuration

To enable SignedPolicy, you need to add the following `<SignedPolicy>` setting in `Server.xml` under `<VirtualHost>`.

```
<VirtualHost>
    <SignedPolicy>
        <PolicyQueryKeyName>policy</PolicyQueryKeyName>
        <SignatureQueryKeyName>signature</SignatureQueryKeyName>
        <SecretKey>aKq#1kj</SecretKey>

        <Enables>
            <Providers>rtmp</Providers>
            <Publishers>webrtc,llhls,thumbnail</Publishers>
        </Enables>
    </SignedPolicy>
</VirtualHost>
```

<table><thead><tr><th width="290">Key</th><th>Description</th></tr></thead><tbody><tr><td>PolicyQueryKeyName</td><td>The query string key name in the URL pointing to the policy value.</td></tr><tr><td>SignatureQueryKeyName</td><td>The query string key name in the URL pointing to the signature value.</td></tr><tr><td>SecretKey</td><td>The secret key used when encoding with HMAC-SHA1.</td></tr><tr><td>Enables</td><td>List of providers and publishers to enable SignedPolicy. Currently, SignedPolicy supports rtmp among providers, and among publishers, WebRTC, LLHLS, Thumbnail are supported.</td></tr></tbody></table>

## Make SignedPolicy URL with a script

We provide a script that can easily generate SignedPolicy URL. The script can be found in the path below.

```
/misc/signed_policy_url_generator.sh
```

Here's how to use this script:

{% code overflow="wrap" %}

```
./signed_policy_generator.sh [HMAC_KEY] [BASE_URL] [SIGNATURE_QUERY_KEY_NAME] [POLICY_QUERY_KEY_NAME] [POLICY]
```

{% endcode %}

For example, you can use it like this:

<figure><img src="https://content.gitbook.com/content/xo7moYXTh3yBG01Dy49w/blobs/VGS9ehrU7IqU8tbzyp9B/image.png" alt=""><figcaption></figcaption></figure>

## Make SignedPolicy URL manually

{% hint style="success" %}
We hope to provide SignedPolicy URL Generator Library in various languages. If you have created the SignedPolicy URL Generator Library in another language, please send a Pull Request to our [GITHUB](https://github.com/AirenSoft/OvenMediaEngine/pulls). Thank you for your open source contributions.
{% endhint %}

### Encoding policy

In order to include the policy in the URL, it must be encoded with [Base64URL](https://tools.ietf.org/html/rfc4648#section-5).

{% code title="Plain {Policy}" %}

```
{"url_expire":1399721581}
```

{% endcode %}

{% code title="Base64URL Encoded {Policy}" %}

```
eyJ1cmxfZXhwaXJlIjoxMzk5NzIxNTgxfQ
```

{% endcode %}

Policy encoded with Base64URL is added as a query string to the existing streaming URL. (The query string key is set in Server.xml.)

```
ws://192.168.0.100:3333/app/stream?policy=eyJ1cmxfZXhwaXJlIjoxMzk5NzIxNTgxfQ
```

### Signature

Signature hashes the entire URL including the policy in HMAC (SHA-1) method, encodes it as Base64URL, and includes it in the query string.

{% code title="URL input to signature generation" %}

```
ws://192.168.0.100:3333/app/stream?policy=eyJ1cmxfZXhwaXJlIjoxMzk5NzIxNTgxfQ
```

{% endcode %}

Create a hash using the secret key (1kU^b6 in the example) and the URL above using HMAC-SHA1.

{% code title="Base64URL encoded { HMAC-SHA1 \<KEY : 1kU^b6> (URL) }" %}

```
dvVdBpoxAeCPl94Kt5RoiqLI0YE
```

{% endcode %}

If you include it as a signature query string (query string key is set in Server.xml), the following SignedPolicy URL is finally generated.

{% code title="URL with signature" overflow="wrap" %}

```
ws://192.168.0.100:3333/app/stream?policy=eyJ1cmxfZXhwaXJlIjoxMzk5NzIxNTgxfQ&signature=dvVdBpoxAeCPl94Kt5RoiqLI0YE
```

{% endcode %}

## Usage examples

### Applying SignedPolicy in OBS

Generate SignedPolicy URL with the script.

<figure><img src="https://content.gitbook.com/content/xo7moYXTh3yBG01Dy49w/blobs/KLCW5CychZ987a7JdluQ/image.png" alt=""><figcaption></figcaption></figure>

Separate the URL based on "app" as shown in the example below and enter all the parts under the stream in the Stream Key.

<figure><img src="https://content.gitbook.com/content/xo7moYXTh3yBG01Dy49w/blobs/Y1IY18fT5ehf54eZCbgh/image.png" alt=""><figcaption></figcaption></figure>