To use these, copy the files into your PostgreSQL 12 Windows 64-bit install folders in same named folders and then run CREATE EXTENSION as usual in the databases of your choice. More details in the packaged README.txt
For those folks on windows who want to do http gets and posts directly from your PostgreSQL server, we've made binaries for the http extension for PostgreSQL Windows.
These should work fine on both PostgreSQL EDB windows distributions as well as the BigSQL windows 64 distributions.
Instructions in the ReadMe.txt for where to copy the files to for each distribution. Caution should be taken especially with BigSQL to not overwrite existing BigSQL files.
Many of the files in this already exist in the BigSQL distribution since we both compile using the Mingw64 chain.
If you have PostGIS already installed, many of these files you will also already have since things like the libcurl and PCRE are also packaged with PostGIS.
PostGIS 3.0.0 is planned for release early next week. In the meantime you will find PostGIS 3.0.0rc1 or rc2 available via yum.postgresql.org, apt.postgresql.org, and EDB Windows 64-bit stackbuilder for PostgreSQL 12.