New functionality: 2-person simultaneous authorization (BBS-96239)

I would like to upload the full source code for a software program. The programmer wants to ensure that I do not have access to it until my final payment is rendered.
That is fine, but I want to make sure that the final source code is placed in BitBucket to protect it.
We agreed to have both authorizations required before either of us can access the code,

i.e. BOTH the programmer authorization and my authorization is needed before the code is available to either of us.