According to IATA:
- Passengers must have a negative COVID-19 test taken at most 72 hours before departure from the first embarkation point. Tests
accepted are: CLEIA/ECLIA quantitative antigen test, LAMP, NEAR, Next
Generation Sequence, PCR, RT-PCR, Smart Amp, TMA or TRC. The test
certificate must be in English and specify that the test is based on a
"nasopharyngeal swab", or "saliva", or "nasopharyngeal and
oropharyngeal swab". A "nasal swab" is also accepted if the test type
is LAMP, NEAR, PCR, RT-PCR, Smart Amp, TMA or TRC. Details can be
found at https://www.mhlw.go.jp/stf/covid-19/border_test.html and
- This does not apply to:
- passengers with a COVID-19 vaccination certificate
The second link only states the following general requirements for the certificate:
A certificate is valid as long as all of the following items are
(1) Name, date of birth
(2) Specimen collected, test method
(3) Result, date and time of specimen collection
(4) Name of medical institution
So as long as whatever test provider you're using can provide a certificate in the requisite format, you're good to go. There's no list of authorized test providers you have to adhere to.
If there is no such list of approved providers, what authentication is performed on the test certificates from any provider?
As of 2023 it's all done solely for the purposes of maintaining a security theater, so there's no authentication whatsoever. No one really cares about the test, they just want to see a piece of paper that satisfies the formal criteria.