Login.gov (a product of USDS and 18F @ GSA) is positioned to meet these identity provider needs.
https://www.login.gov/help/get-started/authentication-option... (2FA support for all users + PIV/CAC support for Fed Gov workers)
https://developers.login.gov/ (developer resources)
Skepticism is warranted as 6 USC 1523: Federal cybersecurity requirements [1] has required a lot of what the EO is calling for for almost half a decade, but the tooling exists and 82 agency applications/systems (as of October 2020) are already leveraging this identity provider. Appropriations ($$$) for this identity integration work seems the challenge, as implementation is straightforward.
Sidenote: You can now login to your Social Security Administration account with Login.gov [2] (under "Other Sign In Options"). If you've applied for TSA Precheck or Global Entry, you've been using Login.gov for some time.
[1] https://uscode.house.gov/view.xhtml?req=granuleid:USC-prelim...
[2] https://secure.ssa.gov/RIL/SiView.action
(disclosure: no affiliation with any federal government agency or office, not a fed gov employee or contractor currently)