Sorry for a fuzzy newbie question but I didn't find a similar yet - maybe I'm just asking wrong..
I'm working on an open source Python application which reads and processes emails from given mailboxes using IMAP and SMTP (from various (self hosted) email providers, so a MS/Google specific implementation is not an option for me). Currently I'm extending that application to support OAuth2 after Microsoft announced they will no longer support standard IMAP/SMTP authorization.
I found lot's of HowTos, tutorials and examples and managed to read/write mails using OAuth2 with GMail-servers now but I hope I just missed the recommended scenario for open source applications.
Currently I've set up a Google "Project" using tutorials I found in order to get ClientID and ClientSecret. Google told me it would cost me $15k to $75k to get my application verified, while Microsoft wants me to create an Azure/Identity Platform account and want's my telephone and credit card number in advance in order to bill me after 12 months.
Question: What am I supposed to provide with my application regarding OAuth2? I don't want to publish my ClientID/Secret do I? Does every user have to go through those registration procedures in order to access its mails using a command line script?
How to other open source mail-applications solve this issue? At least Thunderbird can authenticate with GMail (see https://www.supertechcrew.com/thunderbird-oauth2-gmail/) do they provide ClientID and -secret with the application? Here is an old thread discussing the issue: https://groups.google.com/g/tb-planning/c/RRSPwp36bi0?pli=1
Disclaimer 2: I know this question sounds very obvious but I really didn't find a hint yet :)