This document explains the best way to solve the Bad request - request too long problem when trying to login to Office 365 from Google Chrome.
When trying to reach https://login.microsoftonline.com in Google Chrome the browser instead displays:
Bad Request - Request Too Long
HTTP Error 400. The size of the request headers is too long.
How to fix
In Google Chrome go to > Settings > From the bottom choose "Show Advanced Settings" > Under Privacy Click "Content Settings" > Under Cookies click "All cookies and site data" > Wait for this page to load, once its loaded in the search box to the top right corner type: login.microsoft > Select the entries that come up and use the cross on the right to delete them. This won't delete anything you need. Also search for office and click the cross next to any office.com or office365 entries. Once you've done that, close out and open https://login.microsoftonline.com in a new window and your problem should be solved!
If you don't want to do this yourself please buy a techmates support session and we will fix the problem for you.