MinIO STS: cannot get temporary credentials

Question

I'm following along this guide on how to get temporary credentials from minIO given an access token than I'm currently getting from WSO2.

However, upon reaching step 3 (the actual step that gets the temp credentials from minIO using STS API), I'm getting this error:

<?xml version="1.0" encoding="UTF-8"?>
<Error>
    <Code>XMinioUnknownAPIRequest</Code>
    <Message>Unknown API request at /minio/sts</Message>
    <Resource>/minio/sts</Resource>
    <RequestId></RequestId>
    <HostId>9d60f8b3-f2f3-48f0-94bf-2f416d226a86</HostId>
</Error>

( tested with postman and with curl -X POST -k "{token=<ACCESS_TOKEN>}" -H "Content-Type:application/json" http://localhost:9000/minio/sts, same error on both )

I'm running minIO on docker (minio/minio), MINIO_IDENTITY_OPENID_CONFIG_URL is correctly set and I set MINIO_IDENTITY_OPENID_CLIENT_ID to a random string.

I's there something I'm missing? Do I have to enable STS on minio somehow? thanks