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Wow, we actually did it. 469 days in the making, and some of the toughest in my civic tech career. Here's how we did it. 
https://twitter.com/arouault/status/1362444614200741891
https://twitter.com/arouault/status/1362444614200741891
The journey for me started back in November of 2019 when I naively asked @RobinCarnahan, "So, why *can't* we offer this to state and local governments?" She laid out the basics of federal & state partnerships, and illuminated a path for us.
Our team became experts in the Intergovernmental Cooperation Act of 1968, which we were surprised to find actually *encourages* cooperation between the federal government and states: https://www.govinfo.gov/content/pkg/STATUTE-82/pdf/STATUTE-82-Pg1098.pdf
Title III of the IGCA is short and direct: it authorizes federal agencies to provide specialized and technical services to states and local govs, particularly in support of activities national in scope and federally funded in part, all to avoid "unnecessary duplication."
We then engaged GSA leadership to help us make the pitch to OMB, who ultimately decides if the agency has "special competence" to provide such services, and ensure they are consistent with OMB Circular A-97: https://www.whitehouse.gov/omb/information-for-agencies/circulars/#state
I'll save the details, but it was many months of discussions between GSA and OMB's Office of the Federal Chief Information Officer (OFCIO). Ultimately, they came to an agreement, and set operating parameters. GSA's General Counsel then issued its guidance for the agency.
Our team then prepared detailed rollout and communication plans that many across GSA reviewed. We lost some momentum during the presidential transition (GSA has kind of an important role there), but we picked things right back up after the new administration arrived.
In the days before the public launch, everyone scrambles to make sure all is in place, the website updates are queued up, content is reviewed, forms and emails are working. Then bam — it's live. A small, bureaucratic miracle occurs.
Countless people, past and present, made this possible. In particular, we stood on the shoulders of 18F and the state & local practice they built up over years: https://18f.gsa.gov/tags/state-and-local-practice/
It's worth noting, this is just the *permission* to do the work. Now, we actually have to *do* the work. But that's for tomorrow. Today we celebrate (and get some sleep). 
Parting thoughts: While there will always be some bureaucracy, this took *way* too long. Congress should really consider updating the IGCA (1968) to bring it into the 21st century, and explicitly include "digital services." We have way more to offer: https://digital.gov/services
