Adding Tags via GraphQL API

[xifize]

How do you add/edit a post's tags via the GraphQL API? I was able to login through the API and I assume I'm supposed to use the session string somehow, but I'm not sure exactly how. Here are the queries I tried to use:

Login:

mutation {
  login(username: "user", password: "pass") {
    session
    error
  }
}

This command works and returns a session string.

Adding tags:

mutation {
  update_post_metadata(post_id: 1, metadata: [{key: "tags", value: "tag1, tag2, tag3"}]) {
    id
    tags
  }
}

This command results in no changes. I tried passing an authorization header, but that didn't seem to be right.

[xifize]

You need to set two cookies when sending the HTTP request for the update: shm_session should contain the session string received from the login command, and shm_user should contain your username.