When I tried to set OAuth 2.0 as the authentication method in Incoming Mail settings I realized that it's not on the list:

Then I checked the OAuth 2.0 settings:

I'm not using HTTPS at the moment. Here Running Jira applications over SSL or HTTPS
in the documentation it is said: If you need help with configuring SSL, create a question on the Atlassian community. So, I'd like to know how can I configure HTTPS in order to be able to enable the OAuth 2.0 authentication method?