Hi @Anuraj ,
There isn't API support available just yet. The team is working towards that goal. However, there is a current workaround for using a powershell command, see https://github.com/Azure/azure-powershell/issues/10518. Now I realize powershell isn't the best option; however, perhaps https://learn.microsoft.com/en-us/archive/blogs/kebab/executing-powershell-scripts-from-c will give some ideas on how to execute your powershell from your SaaS.
Furthermore, you should be made aware that app service managed certificates do not support wildcard domains as noted in https://learn.microsoft.com/en-us/azure/app-service/configure-ssl-certificate#create-a-free-certificate-preview.