Blogger detailed instructions:

Basically first you'll need to request the activation from Google of the Blogger API. It takes about 5 working days. Once it's activated you'll need to create your 'Client ID' (aka App) which will auto post on your behalf.
We provide detailed instructions below.

Please go at this url: https://console.developers.google.com/
Then please click on 'API Project' as indicated.

On the left side, click on 'APIs & auth'. The 'APIs' tab is selected by default.

Now you'll ask Google to activate the Blogger API for your account. Scroll down and locate 'Blogger API v3'.
Click the 'OFF' button in order to request the activation.

Fill in the submission form and click 'Submit'.

Google informs you that your request was successfully sent.

After few days you'll receive an email from Google explaining how to complete the activation. Please follow the steps provided by them.
Once you fully activated the Blogger API v3, you need to create your 'Client ID'.
Browse to this url again: https://console.developers.google.com/
Click on 'API Project', then on the left side select 'APIs & auth' -> 'Credentials'
Click on 'Create new Client ID' as indicated.

For 'Application type', select 'Web application'.
For 'Authorized Javascript Origins', enter your blog url (ex: http://www.yourblog.com)
For 'Authorized Redirect Uri', enter the Url when you're on the settings of MicroblogPoster.
It is something like http://www.yourblog.com/wp-admin/options-general.php?page=microblogposter.php
Click 'Create Client ID'.

Copy the Client ID and Client secret and configure your account under MicroblogPoster.

MicroblogPoster will provide you a link in order to authorize the App posting on your behalf.