core.configmanager: Add function for getting secrets from separate filesHEADorigin/mastermaster

Idea is to enable easily retrieving of secret values from files outside
of the config, e.g. via the method used by systemd credentials.

CREDENTIALS_DIRECTORY is expected to be set by the process manager
invoking Prosody, so being unset and unavailable from prosodyctl is
going to be normal and a warning is reported in that case. Care will
have to be taken to make it clear that prosodyctl check will not work
with such values. An error is thrown if the directory is unavailable
when running under Prosody.

3 files changed, 22 insertions, 3 deletions

diff --git a/CHANGES b/CHANGES
index e4f0d269..c7c7e9c9 100644
--- a/CHANGES
+++ b/CHANGES
@@ -60,7 +60,7 @@ TRUNK
 
 - The configuration file now supports referring and appending to options previously set
 - Direct usage of the Lua API in the config file is deprecated, but can now be accessed via Lua.* instead
-- Convenience functions for reading values from files
+- Convenience functions for reading values from files, with variant meant for credentials or secrets
 
 ## Changes
 
diff --git a/core/configmanager.lua b/core/configmanager.lua
index 37a01a84..922ff05f 100644
--- a/core/configmanager.lua
+++ b/core/configmanager.lua
@@ -198,6 +198,7 @@ do
 			FileContents = true,
 			FileLine = true,
 			FileLines = true,
+			Secret = true,
 			Include = true, include = true, RunScript = true }, {
 				__index = function (_, k)
 					if k:match("^ENV_") then
@@ -359,6 +360,19 @@ do
 		env.FileLine = filereader(config_path, "*l");
 		env.FileLines = linereader(config_path);
 
+		if _G.prosody.paths.secrets then
+			env.Secret = filereader(_G.prosody.paths.secrets, "*a");
+		elseif _G.prosody.process_type == "prosody" then
+			env.Secret = function() error("Secret() requires the $CREDENTIALS_DIRECTORY environment variable to be set", 2) end
+		else
+			env.Secret = function()
+				t_insert(warnings, ("%s:%d: Secret() requires the $CREDENTIALS_DIRECTORY environment variable to be set")
+						:format(config_file, get_line_number(config_file)));
+				return nil;
+			end
+
+		end
+
 		local chunk, err = envload(data, "@"..config_file, env);
 
 		if not chunk then
diff --git a/util/startup.lua b/util/startup.lua
index caae895d..1557ab0f 100644
--- a/util/startup.lua
+++ b/util/startup.lua
@@ -266,8 +266,13 @@ function startup.init_global_state()
 	full_sessions = prosody.full_sessions;
 	hosts = prosody.hosts;
 
-	prosody.paths = { source = CFG_SOURCEDIR, config = CFG_CONFIGDIR or ".",
-	                  plugins = CFG_PLUGINDIR or "plugins", data = "data" };
+	prosody.paths = {
+		source = CFG_SOURCEDIR;
+		config = CFG_CONFIGDIR or ".";
+		plugins = CFG_PLUGINDIR or "plugins";
+		data = "data";
+		secrets = os.getenv("CREDENTIALS_DIRECTORY");
+	};
 
 	prosody.arg = _G.arg;