chore(sec): unify usage of crypto/rand.Read (#7453)

- Unify the usage of [`crypto/rand.Read`](https://pkg.go.dev/crypto/rand#Read) to `util.CryptoRandomBytes`.
- Refactor `util.CryptoRandomBytes` to never return an error. It is documented by Go, https://go.dev/issue/66821, to always succeed. So if we still receive a error or if the returned bytes read is not equal to the expected bytes to be read we panic (just to be on the safe side).
- This simplifies a lot of code to no longer care about error handling.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/7453
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: Gusted <postmaster@gusted.xyz>
Co-committed-by: Gusted <postmaster@gusted.xyz>

modules/util/util.go

@@ -88,10 +88,16 @@ func CryptoRandomString(length int64) (string, error) {
 // CryptoRandomBytes generates `length` crypto bytes
 // This differs from CryptoRandomString, as each byte in CryptoRandomString is generated by [0,61] range
 // This function generates totally random bytes, each byte is generated by [0,255] range
-func CryptoRandomBytes(length int64) ([]byte, error) {
+func CryptoRandomBytes(length int64) []byte {
+	// crypto/rand.Read is documented to never return a error.
+	// https://go.dev/issue/66821
 	buf := make([]byte, length)
-	_, err := rand.Read(buf)
-	return buf, err
+	n, err := rand.Read(buf)
+	if err != nil || n != int(length) {
+		panic(err)
+	}
+
+	return buf
 }
 
 // ToUpperASCII returns s with all ASCII letters mapped to their upper case.