[Doc]: New-AzFirewallPolicyApplicationRuleCustomHttpHeader

### Type of issue

Missing information

### Feedback

Hello,

I found documentation to this command: New-AzFirewallPolicyApplicationRuleCustomHttpHeader

https://learn.microsoft.com/en-us/powershell/module/az.network/new-azfirewallpolicyapplicationrulecustomhttpheader?view=azps-11.5.0

This explains the command, but I can't seem to find any documentation as to what this does. I don't even see that this feature exists besides that command. My Expectation is I Create this header and add it to an application rule. Then when this rule is hit the firewall will insert the header. However this doesn't seem to work. My guess is I am doing something wrong, but I have no idea what. Could you maybe add more information on how exactly this works?

For reference, here the application rule I created:

```
SourceAddresses : {*}
TargetFqdns : {login.microsoftonline.com, login.microsoft.com, login.windows.net}
FqdnTags : {}
Protocols : {Microsoft.Azure.Commands.Network.Models.PSAzureFirewallPolicyApplicationRuleProtocol,
Microsoft.Azure.Commands.Network.Models.PSAzureFirewallPolicyApplicationRuleProtocol}
SourceIpGroups : {}
WebCategories : {}
TargetUrls : {}
TerminateTLS : True
HttpHeadersToInsert : {Restrict-Access-To-Tenants, Restrict-Access-Context}
Description :
ProtocolsText : [
{
"protocolType": "Http",
"port": 80
},
{
"protocolType": "Https",
"port": 443
}
]
SourceAddressesText : [
"*"
]
SourceIpGroupsText : []
TargetFqdnsText : [
"login.microsoftonline.com",
"login.microsoft.com",
"login.windows.net"
]
FqdnTagsText : []
WebCategoriesText : []
TargetUrlsText : []
HttpHeadersToInsertText : [
{
"headerName": "Restrict-Access-To-Tenants",
"headerValue": "111fd61c-a2a5-4514-8a8a-f923d46b9b79"
},
{
"headerName": "Restrict-Access-Context",
"headerValue": "111fd61c-a2a5-4514-8a8a-f923d46b9b79"
}
]
Name : restricttenant
RuleType : ApplicationRule

```

### Page URL

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### Content source URL

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### Author

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### Document Id

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Start with the New-AzFirewallPolicyApplicationRuleCustomHttpHeader command reference and the supplied application-rule example. Document what the headers do, how HttpHeadersToInsert is attached to an application rule, and the expected behavior and prerequisites, using the reported Microsoft login endpoints as context; the work is done when a reader can configure and verify the feature without guessing.

Written by the indexing model from the issue text.