Hi Stefan,
I don't think this is explained well online, I'll be adding instructions shortly. For now:
When you want to send a verification email (probably right after sign up), you can get the Oob Confirmation code from the
Oob API call. Note that you don't need to provide the reCAPTCHA challenge & response info here. This RPC must be signed by your service account in a similar manner to the way you would for an
email change - these instructions are relatively complicated, so it might be worth looking at how we get the OAuth2 tokens in one of our client libraries.
Once you have the Oob code, you should embed it in a link that you send to your user. When they click on the link, you can include that Oob code in a call to
setAccountInfo with the param "emailVerified" set to true.
Hope this helps. Please let us know if you have any more issues.