GET requests with Web connector

I need to load csv files from AWS S3.

Unlike this question, I am using a signed url to access the data. The url works in fine in the webbrowser, but in Power BI desktop Web connector it throws the following exception: 

DataSource.Error: Web.Contents failed to get contents from 'https://s3.<signed url>' (400): Bad Request
Details:
    DataSourceKind=Web
    DataSourcePath=https://s3.<signed url>

Does anyone know what the reason for that is?