How to login to an own android APP


I have a question. I have already searched for a while.
It is possible to login to my app at the moment, but just at the first time with name and password and then just a click.
What I want is, that I have to Textfields in my app for name and password and the app will login with these datas.
I hope anyone can help me with a sample Code.
Thank you very much


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