Did you take a look at this answer? There are a few tools listed.
However the key point for you is to have a certificate that your client will accept. To answer your question, in its simplest form you need:
- A valid SSL certificate (signed by the CAs that are trusted by the client)
- Control of DNS resolution (but if you control the environment you'd have your tool set up on the gateway, as suggested in the comments)
A possible scenario would be:
With DNS resolution:
- Client looks up server IP
- Your DNS resolves it to the IP address of your tool
Client connects to your tool
- Your tool responds with a signed certificate for the requested hostname
- Profit! Also, MiTM
A slightly modified version of this set up is to install on your client the certificate of your own CA, with which you can sign the SSL certificate of your tool. Since you talk about 'authorised' SSL stripping, I assume you have control of the client environment.