There may not be a quick way to do this from Azure portal directly.
Look at this blog from Feb, 2018 about a PowerShell module created to tackle exactly this kind of scenarios by Azure Rapid Response team.
Use AzureRMAppGWCert to list certificate details of Azure App Gateway
![enter image description here](https://i.stack.imgur.com/p03Au.png)
This Module is Published at https://www.powershellgallery.com/packages/AzureRMAppGWCert
In order to install just open the powershell as Administrator and type:
Install-Module AzureRMAppGWCert
Import-Module AzureRMAppGWCert
Example: Listing all digital certificates associated with a single Application Gateway:
This Module will list all certificates associated with Application Gateway and generate an output like this:
PS C:\> Get-AzureRMAppGWCert -RG OfficeClient -AppGWName AppGateway
AppGWName : AppGateway
ListnerName : appGatewayHttpListener
Subject : CN=*.hepoca.com, O=Hepoca Armarios e Servicos Ltda - EPP, L=Taguatinga, S=Distrito Federal, C=BR
Issuer : CN=DigiCert SHA2 Secure Server CA, O=DigiCert Inc, C=US
SerialNumber : 0E99D5E2EBBE329CFE2DDE29C1D7D343
Thumbprint : 5FD6F2A7BC4BD095198AE55D1A0A76D46365C6B9
NotBefore : 3/13/2017 7:00:00 PM
NotAfter : 5/2/2018 7:00:00 AM
AppGWName : AppGateway
ListnerName : HTTPs8080
Subject : CN=*.hepoca.com, O=Hepoca Armarios e Servicos Ltda - EPP, L=Taguatinga, S=Distrito Federal, C=BR
Issuer : CN=DigiCert SHA2 Secure Server CA, O=DigiCert Inc, C=US
SerialNumber : 0E99D5E2EBBE329CFE2DDE29C1D7D343
Thumbprint : 5FD6F2A7BC4BD095198AE55D1A0A76D46365C6B9
NotBefore : 3/13/2017 7:00:00 PM
NotAfter : 5/2/2018 7:00:00 AM
AppGWName : AppGateway
HTTPSetting : appGatewayBackendHttpSettings
RuleName : rule1
BackendCertName : webjson-pub
Subject : [email protected], CN=webjson.arr.local, OU=Arr, O=ARR, L=Irving, S=TX, C=US
Issuer : [email protected], CN=webjson.arr.local, OU=Arr, O=ARR, L=Irving, S=TX, C=US
SerialNumber : 00B1722AB4D0FB8CAA
Thumbprint : 573C70769A40CF4D01769926A212009598462436
NotBefore : 11/28/2017 12:45:23 PM
NotAfter : 11/28/2018 12:45:23 PM