Write down a formal GSS-TSIG design

We have many notes and an idea how the GSS-TSIG hook will look like. We need to write a formal design for it. This is required for several reasons:

• the customer has to review the design. This should be done early, so there is enough time to address comments
• all participating engineers are on the same page and have the same understanding of the ultimate goal
• the IT dept needs time in advance to set up the test environment
• the QA dept needs time in advance to develop the tests