Relative path for pfx certificate for SharePoint provider hosted apps

I have created a provider hosted app where i m referring certificate from app.config file,which is a local path,how do it make it relative pathso that certificate is referred without hard coding the local path.

<add key="ClientSigningCertificatePath" value="D:\Certificates\testabdfrrrr.cloudnet.net.pfx" />
    <add key="ClientSigningCertificatePassword" value="online" />
    <add key="IssuerId" value="cd8dfs94-f82f-4ea0-9be5-d41276age59a" />

Using Tokenhelper.cs file for getting current client context for SharePoint provider hosted apps