Do I have to be Discord-Server owner/admin?

[Ismoh]

Is it possible to post a message on any discord server I like or do I have to be admin to create and provide the webhook url?
Can I use my discord credentials to post a message with my discord account?

To clarify stuff:
I am implementing a mod for a specific game. There is a discord server for this game with a mod-release channel, where I would like to post a message everytime there is a new tag/release on github.

Any possibility to do so? (Because I am lazy and love to automate stuff)

Thanks in advantage!