Always load or generate oauth2 jwt secret (#30942)

Fix #30923

routers/install/install.go

@@ -481,6 +481,17 @@ func SubmitInstall(ctx *context.Context) {
 		cfg.Section("security").Key("INTERNAL_TOKEN").SetValue(internalToken)
 	}
 
+	// FIXME: at the moment, no matter oauth2 is enabled or not, it must generate a "oauth2 JWT_SECRET"
+	// see the "loadOAuth2From" in "setting/oauth2.go"
+	if !cfg.Section("oauth2").HasKey("JWT_SECRET") && !cfg.Section("oauth2").HasKey("JWT_SECRET_URI") {
+		_, jwtSecretBase64, err := generate.NewJwtSecretWithBase64()
+		if err != nil {
+			ctx.RenderWithErr(ctx.Tr("install.secret_key_failed", err), tplInstall, &form)
+			return
+		}
+		cfg.Section("oauth2").Key("JWT_SECRET").SetValue(jwtSecretBase64)
+	}
+
 	// if there is already a SECRET_KEY, we should not overwrite it, otherwise the encrypted data will not be able to be decrypted
 	if setting.SecretKey == "" {
 		var secretKey string