Noodling with the GitHub PAT checksum

github-pat-checksum.R

pat <- gitcreds::gitcreds_get()
cksum <- digest::digest(
  substr(pat$password, start = 5, stop = nchar(pat$password) - 6),
  algo =  "crc32", serialize = FALSE
)

# https://stackoverflow.com/q/5478508
toBase <- function(num, base=62) {
  # bv <- c(seq(0,9),letters,LETTERS)
  # GitHub seems to do UPPERCASE then lowercase
  bv <- c(seq(0,9), LETTERS, letters)
  r <- num %% base
  res <- bv[r+1]
  q <- floor(num/base)
  while (q > 0L) {
    r <- q %% base
    q  <- floor(q/base)
    res <- paste(bv[r+1], res, sep='')
  }
  res
} 
to10 <- function(num, base=62) {
  bv <- c(seq(0,9),letters,LETTERS)
  vb <- list()
  for (i in 1:length(bv)) vb[[bv[i]]] <- i
  num <- strsplit(num,'')[[1]]
  res <- vb[[num[1]]]-1
  if (length(num) > 1)
    for (i in 2:length(num)) res <- base * res + (vb[[num[i]]]-1)
  res
}

(expected <- toBase(to10(cksum, base = 16)))
(actual <- substr(pat$password, start = 35, stop = 40))
testthat::expect_equal(expected, actual)