This is the new *Amazon CloudFormation Template Reference Guide*. Please update your bookmarks and links. For help getting started with CloudFormation, see the [Amazon CloudFormation User Guide](https://docs.amazonaws.cn/AWSCloudFormation/latest/UserGuide/Welcome.html).

# AWS::WAFv2::WebACL Headers
<a name="aws-properties-wafv2-webacl-headers"></a>

Inspect all headers in the web request. You can specify the parts of the headers to inspect and you can narrow the set of headers to inspect by including or excluding specific keys.

This is used to indicate the web request component to inspect, in the `FieldToMatch` specification. 

If you want to inspect just the value of a single header, use the `SingleHeader``FieldToMatch` setting instead.

Example JSON: `"Headers": { "MatchPattern": { "All": {} }, "MatchScope": "KEY", "OversizeHandling": "MATCH" }`

## Syntax
<a name="aws-properties-wafv2-webacl-headers-syntax"></a>

To declare this entity in your Amazon CloudFormation template, use the following syntax:

### JSON
<a name="aws-properties-wafv2-webacl-headers-syntax.json"></a>

```
{
  "[MatchPattern](#cfn-wafv2-webacl-headers-matchpattern)" : HeaderMatchPattern,
  "[MatchScope](#cfn-wafv2-webacl-headers-matchscope)" : String,
  "[OversizeHandling](#cfn-wafv2-webacl-headers-oversizehandling)" : String
}
```

### YAML
<a name="aws-properties-wafv2-webacl-headers-syntax.yaml"></a>

```
  [MatchPattern](#cfn-wafv2-webacl-headers-matchpattern): 
    HeaderMatchPattern
  [MatchScope](#cfn-wafv2-webacl-headers-matchscope): String
  [OversizeHandling](#cfn-wafv2-webacl-headers-oversizehandling): String
```

## Properties
<a name="aws-properties-wafv2-webacl-headers-properties"></a>

`MatchPattern`  <a name="cfn-wafv2-webacl-headers-matchpattern"></a>
The filter to use to identify the subset of headers to inspect in a web request.   
You must specify exactly one setting: either `All`, `IncludedHeaders`, or `ExcludedHeaders`.  
Example JSON: `"MatchPattern": { "ExcludedHeaders": [ "KeyToExclude1", "KeyToExclude2" ] }`  
*Required*: Yes  
*Type*: [HeaderMatchPattern](aws-properties-wafv2-webacl-headermatchpattern.md)  
*Update requires*: [No interruption](https://docs.amazonaws.cn/AWSCloudFormation/latest/UserGuide/using-cfn-updating-stacks-update-behaviors.html#update-no-interrupt)

`MatchScope`  <a name="cfn-wafv2-webacl-headers-matchscope"></a>
The parts of the headers to match with the rule inspection criteria. If you specify `ALL`, Amazon WAF inspects both keys and values.   
`All` does not require a match to be found in the keys and a match to be found in the values. It requires a match to be found in the keys or the values or both. To require a match in the keys and in the values, use a logical `AND` statement to combine two match rules, one that inspects the keys and another that inspects the values.   
*Required*: Yes  
*Type*: String  
*Allowed values*: `ALL | KEY | VALUE`  
*Update requires*: [No interruption](https://docs.amazonaws.cn/AWSCloudFormation/latest/UserGuide/using-cfn-updating-stacks-update-behaviors.html#update-no-interrupt)

`OversizeHandling`  <a name="cfn-wafv2-webacl-headers-oversizehandling"></a>
What Amazon WAF should do if the headers determined by your match scope are more numerous or larger than Amazon WAF can inspect. Amazon WAF does not support inspecting the entire contents of request headers when they exceed 8 KB (8192 bytes) or 200 total headers. The underlying host service forwards a maximum of 200 headers and at most 8 KB of header contents to Amazon WAF.   
The options for oversize handling are the following:  
+ `CONTINUE` - Inspect the available headers normally, according to the rule inspection criteria. 
+ `MATCH` - Treat the web request as matching the rule statement. Amazon WAF applies the rule action to the request.
+ `NO_MATCH` - Treat the web request as not matching the rule statement.
*Required*: Yes  
*Type*: String  
*Allowed values*: `CONTINUE | MATCH | NO_MATCH`  
*Update requires*: [No interruption](https://docs.amazonaws.cn/AWSCloudFormation/latest/UserGuide/using-cfn-updating-stacks-update-behaviors.html#update-no-interrupt)

## Examples
<a name="aws-properties-wafv2-webacl-headers--examples"></a>



### Set the Headers specification
<a name="aws-properties-wafv2-webacl-headers--examples--Set_the_Headers_specification"></a>

The following shows an example Headers field to match specification. 

#### YAML
<a name="aws-properties-wafv2-webacl-headers--examples--Set_the_Headers_specification--yaml"></a>

```
FieldToMatch:
  Headers:
    MatchPattern:
      IncludedHeaders:
      - "User-Agent"
      - "Referer"
    MatchScope: ALL 
    OversizeHandling: MATCH
```

#### JSON
<a name="aws-properties-wafv2-webacl-headers--examples--Set_the_Headers_specification--json"></a>

```
"FieldToMatch": {
  "Headers": {
    "MatchPattern": {
      "IncludedHeaders": [
        "User-Agent",
        "Referer"
      ]
    },
    "MatchScope": "ALL",
    "OversizeHandling": "MATCH" 
  }
}
```