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/setting/oauth2.go

@@ -138,10 +138,7 @@ func loadOAuth2From(rootCfg ConfigProvider) {
 	if InstallLock {
 		jwtSecretBytes, err := generate.DecodeJwtSecret(jwtSecretBase64)
 		if err != nil {
-			jwtSecretBytes, jwtSecretBase64, err = generate.NewJwtSecret()
-			if err != nil {
-				log.Fatal("error generating JWT secret: %v", err)
-			}
+			jwtSecretBytes, jwtSecretBase64 = generate.NewJwtSecret()
 			saveCfg, err := rootCfg.PrepareSaving()
 			if err != nil {
 				log.Fatal("save oauth2.JWT_SECRET failed: %v", err)
@@ -161,10 +158,7 @@ var generalSigningSecret atomic.Pointer[[]byte]
 func GetGeneralTokenSigningSecret() []byte {
 	old := generalSigningSecret.Load()
 	if old == nil || len(*old) == 0 {
-		jwtSecret, _, err := generate.NewJwtSecret()
-		if err != nil {
-			log.Fatal("Unable to generate general JWT secret: %v", err)
-		}
+		jwtSecret, _ := generate.NewJwtSecret()
 		if generalSigningSecret.CompareAndSwap(old, &jwtSecret) {
 			return jwtSecret
 		}