Port of https://github.com/go-gitea/gitea/pull/29205
Use a clearly defined "signing secret" for token signing.
(cherry picked from commit 8be198cdef0a486f417663b1fd6878458d7e5d92)
* Use single shared random string generation function
- Replace 3 functions that do the same with 1 shared one
- Use crypto/rand over math/rand for a stronger RNG
- Output only alphanumerical for URL compatibilty
Fixes: #15536
* use const string method
* Update modules/avatar/avatar.go
Co-authored-by: a1012112796 <1012112796@qq.com>
Co-authored-by: a1012112796 <1012112796@qq.com>
TheFox0x7