I would like to develop only for myself (not for other users). Is there the concept of personal access tokens like many other APIs have for this purpose so I don't have to build the oauth flow just to get my own data? Examples of companies having this are Airtable and Github.
For starters you can use the personal access token in your API page in your settings (browser only) but with that you can only get your athlete infos. If you want more you have to use the OAuth flow.