My question is stupidly simple: how do you log in to Nexus Repository Manager at https://oss.sonatype.org/?

Longer explanation:

I’m trying to debug why ./gradlew publish fails with the a 401 error:

Execution failed for task ':initializeSonatypeStagingRepository'.
> Failed to load staging profiles, server at https://oss.sonatype.org/service/local/ responded with status code 401, body: 

I have the following in my build.gradle.kts

plugins {
    id("io.github.gradle-nexus.publish-plugin") version "2.0.0"
    id("maven-publish")
    id("signing")
}

nexusPublishing {
    repositories {
        sonatype {
            val baseUrl = "https://oss.sonatype.org"
            nexusUrl.set(URI("$baseUrl/service/local/"))
            snapshotRepositoryUrl.set(URI("$baseUrl/content/repositories/snapshots/"))
            username.set(System.getenv("SONATYPE_USER"))
            password.set(System.getenv("SONATYPE_PASSWORD"))
        }
    }
}

I figured the very first thing I should do is manually make sure my SONATYPE_USER and SONATYPE_PASSWORD actually work, so I head on over to https://oss.sonatype.org/ and click log in.

When I created a Sonatype account at https://central.sonatype.com/api/auth/login, I created it through GitHub. Alas, on https://oss.sonatype.org/ there is no option to sign in via GitHub, so I try using the user token I generated at https://central.sonatype.com/account, but it is rejected.

There’s no option to create an account or reset a forgotten password, and when you fail to log in, the error message tells you to log in again before making further requests (?!).

Surprisingly, I couldn’t find anything in their documentation explaining how to do this. And of course before coming here to StackOverflow, I tried contacting their support, but my ticket was immediately closed because I’m not a paying customer.

So, how exactly are you supposed to log in?