I just wanted to thank you both @jofas and @firebits.io
I thought your sayings about extracting json, custom claim in jwt and parsing url instead of body.
Since I'm building this kind of thing for first time in Rust. I couldn't realize that my design may be able to create problem in the future. As you said code smell.
I'm planning to do some changes on my architecture.
I could do it silently but I wanted to say thank you.