Swagger is locked when using the `checkAuth` filter example from docs

Describe the bug When using the example for authentication the Swagger page is locked. Is this intentional, and is there a recommended way to enable docs without introducing state etc.?

To Reproduce This is a simple API taken from plumber documentation

library(plumber)

#* @apiTitle Plumber Example API
#* @apiDescription Plumber example description.
#* @filter setuser
function(req) {
  un <- req$cookies$user
  # Make req$username available to endpoints
  req$username <- un
  plumber::forward()
}

#* @filter checkAuth
function(req, res) {
  if (is.null(req$username)){
    res$status <- 401 # Unauthorized
    return(list(error="Authentication required"))
  } else {
    plumber::forward()
  }
}

#* Echo back the input
#* @param msg The message to echo
#* @get /echo
function(msg = "") {
    list(msg = paste0("The message is: '", msg, "'"))
}

Expected behavior Swagger docs are rendered

Screenshots

CLI (please complete the following information):

OS: Ubuntu
Version 22.04.3 LTS

Additional context

R version 4.3.1 (2023-06-16)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 22.04.3 LTS

Matrix products: default
BLAS:   /usr/lib/x86_64-linux-gnu/openblas-pthread/libblas.so.3 
LAPACK: /usr/lib/x86_64-linux-gnu/openblas-pthread/libopenblasp-r0.3.20.so;  LAPACK version 3.10.0

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C               LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8     LC_MONETARY=en_US.UTF-8   
 [6] LC_MESSAGES=en_US.UTF-8    LC_PAPER=en_US.UTF-8       LC_NAME=C                  LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

time zone: Etc/UTC
tzcode source: system (glibc)

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] jsonlite_1.8.7   purrr_1.0.2      rlang_1.1.1      plumber_1.2.1    conflicted_1.2.0

loaded via a namespace (and not attached):
 [1] later_1.3.1       R6_2.5.1          httpuv_1.6.11     fastmap_1.1.1     swagger_3.33.1    magrittr_2.0.3    webutils_1.2.0    cachem_1.0.8     
 [9] memoise_2.0.1     lifecycle_1.0.3   promises_1.2.1    cli_3.6.1         vctrs_0.6.5       rsconnect_1.1.0   compiler_4.3.1    rstudioapi_0.15.0
[17] tools_4.3.1       ellipsis_0.3.2    Rcpp_1.0.11       stringi_1.7.12

streamdal / plumber

Swagger is locked when using the `checkAuth` filter example from docs #366