Avoid permissions errors for chown .well-known

When acme.sh is run as a non-root user different from the owner of the
webroot directory it is unable to change the owner of the files in
.well-known to that user, causing permissions errors.  Avoid this by
making the files world-readable.

These files should pose no disclosure risk since they are sent in
cleartext during the HTTP Identifier Validation Challenge[1] and may
already be exposed by directory enumeration, depending on server
settings.  AFAIK they should be safe to expose as world-readable in all
cases.

1.  https://ietf-wg-acme.github.io/acme/#rfc.section.7.2

Fixes Neilpang/acme.sh#32
Signed-off-by: Kevin Locke <kevin@kevinlocke.name>

acme.sh

@@ -5002,9 +5002,11 @@ $_authorizations_map"
 
         _debug "Writing token: $token to $wellknown_path/$token"
 
-        mkdir -p "$wellknown_path"
-
-        if ! printf "%s" "$keyauthorization" >"$wellknown_path/$token"; then
+        # Ensure .well-known is visible to web server user/group
+        # https://github.com/Neilpang/acme.sh/pull/32
+        if ! (umask ugo+rx &&
+          mkdir -p "$wellknown_path" &&
+          printf "%s" "$keyauthorization" >"$wellknown_path/$token"); then
           _err "$d: Cannot write token to file: $wellknown_path/$token"
           _clearupwebbroot "$_currentRoot" "$removelevel" "$token"
           _clearup