In regard to WordPress post paged, I would use /player-12345 or other structure as url specific page rather than /player/12345.
How to create new url structure for page
Creating additional url structure, you need WP_Rewrite, there are a couple of filters that you can fire with your function. For Page, you can filter page_rewrite_rules. See example code on ...
I'd recommend Auth0 plugin https://wordpress.org/plugins/auth0/
oAuth plugins should auto populate the data that your API call allows. And your users should be able to edit their profiles also.
LinkedIn also has an AutoFill function here: https://docs.microsoft.com/en-us/linkedin/consumer/integrations/self-serve/plugins/autofill-plugin