Hi Kpop,
I am not sure if you are aware of this, but Method actually has a Contacts Portal built right into all Method Accounts. If you want more info on the Method Contacts Portal, take a look at this Help Center Article. The basic Contacts Portal in Method gives you a place that your Customers would be able to login to into, in order to look at their transactions, make payments for their account, update their Contact Info and many more. This Portal is customizable, if you want to add additional features/functionality that aren't already in the Portal, you can do this.
With that said, if you are looking to use a 3rd party CMS software, Method doesn't have any specific integrations with any CMS Sofware Providers. However, Method does have an open API, if it is a must to integrate with a 3rd party CMS Software provider, you can likely create an application that would allow for both to integrate.
-Ben