Add special handling for httr2_oauth_parse errors.

Picks up on the special error class introduced in r-lib/httr2#596.

This substantially improves the error message when there are
misconfigurations on the Connect side.

This commit does not update the snapshots so that tests continue to pass
with the CRAN version of httr2.

Signed-off-by: Aaron Jacobs <aaron.jacobs@posit.co>

R/viewer-based-credentials.R

@@ -54,6 +54,23 @@ connect_viewer_token <- function(session,
       # Don't use the cached token when testing.
       reauth = is_testing()
     ),
+    httr2_oauth_parse = function(cnd) {
+      # The original implementation of viewer-based credentials returned a
+      # regular Connect error response, which httr2 doesn't understand. Try to
+      # turn it into a useful message in that case.
+      body <- try(resp_body_json(cnd$resp), TRUE)
+      if (inherits(body, "try-error") || !has_name(body, "error_message")) {
+        # Re-throw errors we don't expect.
+        stop(cnd)
+      }
+      # Emulate httr2:::oauth_flow_abort().
+      cli::cli_abort(c(
+          "OAuth failure [invalid_request]",
+          "*" = body$error_message,
+          i = if (body$error_code == 212) "Learn more at \
+          {.url https://docs.posit.co/connect/user/oauth-integrations/#adding-oauth-integrations-to-deployed-content}."
+      ), call = NULL)
+    },
     error = function(cnd) {
       cli::cli_abort(
         "Cannot fetch viewer-based credentials for the current Shiny session.",