Merge bitcoin/bitcoin#28167: init: Add option for rpccookie permissions (replace 26088)

73f0a6cbd0 doc: detail -rpccookieperms option (willcl-ark)
d2afa2690c test: add rpccookieperms test (willcl-ark)
f467aede78 init: add option for rpccookie permissions (willcl-ark)
7df03f1a92 util: add perm string helper functions (willcl-ark)

Pull request description:

  This PR picks up #26088 by aureleoules which adds a bitcoind launch option `-rpccookieperms` to set the file permissions of the cookie generated by bitcoin core.

  Example usage to make the generated cookie group-readable: `./src/bitcoind -rpccookieperms=group`.

  Accepted values for `-rpccookieperms` are `[owner|group|all]`. We let `fs::perms` handle platform-specific permissions changes.

ACKs for top commit:
  achow101:
    ACK 73f0a6cbd0
  ryanofsky:
    Code review ACK 73f0a6cbd0. Main change since last review is no longer throwing a skip exception in the rpc test on windows, so other checks can run after it, and overall test result is passing, not skipped. Also were clarifying renames and documentation improvements.
  tdb3:
    cr ACK 73f0a6cbd0

Tree-SHA512: e800d59a44aca10e1c58ca69bf3fdde9f6ccf5eab4b7b962645af6d6bc0cfa3a357701e409c8c60d8d7744fcd33a91e77ada11790aa88cd7811ef60fab86ab11

src/httprpc.cpp

@@ -11,6 +11,8 @@
 #include <netaddress.h>
 #include <rpc/protocol.h>
 #include <rpc/server.h>
+#include <util/fs.h>
+#include <util/fs_helpers.h>
 #include <util/strencodings.h>
 #include <util/string.h>
 #include <walletinitinterface.h>
@@ -19,6 +21,7 @@
 #include <iterator>
 #include <map>
 #include <memory>
+#include <optional>
 #include <set>
 #include <string>
 #include <vector>
@@ -291,8 +294,20 @@ static bool InitRPCAuthentication()
 {
     if (gArgs.GetArg("-rpcpassword", "") == "")
     {
-        LogPrintf("Using random cookie authentication.\n");
-        if (!GenerateAuthCookie(&strRPCUserColonPass)) {
+        LogInfo("Using random cookie authentication.\n");
+
+        std::optional<fs::perms> cookie_perms{std::nullopt};
+        auto cookie_perms_arg{gArgs.GetArg("-rpccookieperms")};
+        if (cookie_perms_arg) {
+            auto perm_opt = InterpretPermString(*cookie_perms_arg);
+            if (!perm_opt) {
+                LogInfo("Invalid -rpccookieperms=%s; must be one of 'owner', 'group', or 'all'.\n", *cookie_perms_arg);
+                return false;
+            }
+            cookie_perms = *perm_opt;
+        }
+
+        if (!GenerateAuthCookie(&strRPCUserColonPass, cookie_perms)) {
             return false;
         }
     } else {