auth: add basic authentication filter framework

This leverages the new lua support. See
filters/simple-authentication.lua for explaination of how this works.
There is also additional documentation in cgitrc.5.txt.

Though this is a cookie-based approach, cgit's caching mechanism is
preserved for authenticated pages.

Very plugable and extendable depending on user needs.

The sample script uses an HMAC-SHA1 based cookie to store the
currently logged in user, with an expiration date.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

6 files changed, 387 insertions, 16 deletions

diff --git a/cgit.c b/cgit.c
index f3fe56b..c52ef33 100644
--- a/cgit.c
+++ b/cgit.c
@@ -192,6 +192,8 @@ static void config_cb(const char *name, const char *value)
                 ctx.cfg.commit_filter = cgit_new_filter(value, COMMIT);
         else if (!strcmp(name, "email-filter"))
                 ctx.cfg.email_filter = cgit_new_filter(value, EMAIL);
+        else if (!strcmp(name, "auth-filter"))
+                ctx.cfg.auth_filter = cgit_new_filter(value, AUTH);
         else if (!strcmp(name, "embedded"))
                 ctx.cfg.embedded = atoi(value);
         else if (!strcmp(name, "max-atom-items"))
@@ -378,6 +380,10 @@ static void prepare_context(struct cgit_context *ctx)
         ctx->env.script_name = getenv("SCRIPT_NAME");
         ctx->env.server_name = getenv("SERVER_NAME");
         ctx->env.server_port = getenv("SERVER_PORT");
+        ctx->env.http_cookie = getenv("HTTP_COOKIE");
+        ctx->env.http_referer = getenv("HTTP_REFERER");
+        ctx->env.content_length = getenv("CONTENT_LENGTH") ? strtoul(getenv("CONTENT_LENGTH"), NULL, 10) : 0;
+        ctx->env.authenticated = 0;
         ctx->page.mimetype = "text/html";
         ctx->page.charset = PAGE_ENCODING;
         ctx->page.filename = NULL;
@@ -593,11 +599,92 @@ static int prepare_repo_cmd(struct cgit_context *ctx)
         return 0;
 }
 
+static inline void open_auth_filter(struct cgit_context *ctx, const char *function)
+{
+        cgit_open_filter(ctx->cfg.auth_filter, function,
+                ctx->env.http_cookie ? ctx->env.http_cookie : "",
+                ctx->env.request_method ? ctx->env.request_method : "",
+                ctx->env.query_string ? ctx->env.query_string : "",
+                ctx->env.http_referer ? ctx->env.http_referer : "",
+                ctx->env.path_info ? ctx->env.path_info : "",
+                ctx->env.http_host ? ctx->env.http_host : "",
+                ctx->env.https ? ctx->env.https : "",
+                ctx->qry.repo ? ctx->qry.repo : "",
+                ctx->qry.page ? ctx->qry.page : "",
+                ctx->qry.url ? ctx->qry.url : "");
+}
+
+#define MAX_AUTHENTICATION_POST_BYTES 4096
+static inline void authenticate_post(struct cgit_context *ctx)
+{
+        if (ctx->env.http_referer && strlen(ctx->env.http_referer) > 0) {
+                html("Status: 302 Redirect\n");
+                html("Cache-Control: no-cache, no-store\n");
+                htmlf("Location: %s\n", ctx->env.http_referer);
+        } else {
+                html("Status: 501 Missing Referer\n");
+                html("Cache-Control: no-cache, no-store\n\n");
+                exit(0);
+        }
+
+        open_auth_filter(ctx, "authenticate-post");
+        char buffer[MAX_AUTHENTICATION_POST_BYTES];
+        int len;
+        len = ctx->env.content_length;
+        if (len > MAX_AUTHENTICATION_POST_BYTES)
+                len = MAX_AUTHENTICATION_POST_BYTES;
+        if (read(STDIN_FILENO, buffer, len) < 0)
+                die_errno("Could not read POST from stdin");
+        if (write(STDOUT_FILENO, buffer, len) < 0)
+                die_errno("Could not write POST to stdout");
+        /* The filter may now spit out a Set-Cookie: ... */
+        cgit_close_filter(ctx->cfg.auth_filter);
+
+        html("\n");
+        exit(0);
+}
+
+static inline void authenticate_cookie(struct cgit_context *ctx)
+{
+        /* If we don't have an auth_filter, consider all cookies valid, and thus return early. */
+        if (!ctx->cfg.auth_filter) {
+                ctx->env.authenticated = 1;
+                return;
+        }
+
+        /* If we're having something POST'd to /login, we're authenticating POST,
+         * instead of the cookie, so call authenticate_post and bail out early.
+         * This pattern here should match /?p=login with POST. */
+        if (ctx->env.request_method && ctx->qry.page && !ctx->repo && \
+            !strcmp(ctx->env.request_method, "POST") && !strcmp(ctx->qry.page, "login")) {
+                authenticate_post(ctx);
+                return;
+        }
+
+        /* If we've made it this far, we're authenticating the cookie for real, so do that. */
+        open_auth_filter(ctx, "authenticate-cookie");
+        ctx->env.authenticated = cgit_close_filter(ctx->cfg.auth_filter);
+}
+
 static void process_request(void *cbdata)
 {
         struct cgit_context *ctx = cbdata;
         struct cgit_cmd *cmd;
 
+        /* If we're not yet authenticated, no matter what page we're on,
+         * display the authentication body from the auth_filter. This should
+         * never be cached. */
+        if (!ctx->env.authenticated) {
+                ctx->page.title = "Authentication Required";
+                cgit_print_http_headers(ctx);
+                cgit_print_docstart(ctx);
+                cgit_print_pageheader(ctx);
+                open_auth_filter(ctx, "body");
+                cgit_close_filter(ctx->cfg.auth_filter);
+                cgit_print_docend();
+                return;
+        }
+
         cmd = cgit_get_cmd(ctx);
         if (!cmd) {
                 ctx->page.title = "cgit error";
@@ -911,6 +998,7 @@ int main(int argc, const char **argv)
         int err, ttl;
 
         cgit_init_filters();
+        atexit(cgit_cleanup_filters);
 
         prepare_context(&ctx);
         cgit_repolist.length = 0;
@@ -948,18 +1036,22 @@ int main(int argc, const char **argv)
                 cgit_parse_url(ctx.qry.url);
         }
 
+        /* Before we go any further, we set ctx.env.authenticated by checking to see
+         * if the supplied cookie is valid. All cookies are valid if there is no
+         * auth_filter. If there is an auth_filter, the filter decides. */
+        authenticate_cookie(&ctx);
+
         ttl = calc_ttl();
         if (ttl < 0)
                 ctx.page.expires += 10 * 365 * 24 * 60 * 60; /* 10 years */
         else
                 ctx.page.expires += ttl * 60;
-        if (ctx.env.request_method && !strcmp(ctx.env.request_method, "HEAD"))
+        if (!ctx.env.authenticated || (ctx.env.request_method && !strcmp(ctx.env.request_method, "HEAD")))
                 ctx.cfg.nocache = 1;
         if (ctx.cfg.nocache)
                 ctx.cfg.cache_size = 0;
         err = cache_process(ctx.cfg.cache_size, ctx.cfg.cache_root,
                             ctx.qry.raw, ttl, process_request, &ctx);
-        cgit_cleanup_filters();
         if (err)
                 cgit_print_error("Error processing page: %s (%d)",
                                  strerror(err), err);
diff --git a/cgit.h b/cgit.h
index e200a06..496d0f6 100644
--- a/cgit.h
+++ b/cgit.h
@@ -53,7 +53,7 @@ typedef void (*filepair_fn)(struct diff_filepair *pair);
 typedef void (*linediff_fn)(char *line, int len);
 
 typedef enum {
-        ABOUT, COMMIT, SOURCE, EMAIL
+        ABOUT, COMMIT, SOURCE, EMAIL, AUTH
 } filter_type;
 
 struct cgit_filter {
@@ -252,6 +252,7 @@ struct cgit_config {
         struct cgit_filter *commit_filter;
         struct cgit_filter *source_filter;
         struct cgit_filter *email_filter;
+        struct cgit_filter *auth_filter;
 };
 
 struct cgit_page {
@@ -278,6 +279,10 @@ struct cgit_environment {
         const char *script_name;
         const char *server_name;
         const char *server_port;
+        const char *http_cookie;
+        const char *http_referer;
+        unsigned int content_length;
+        int authenticated;
 };
 
 struct cgit_context {
diff --git a/cgitrc.5.txt b/cgitrc.5.txt
index 170e825..c45dbd3 100644
--- a/cgitrc.5.txt
+++ b/cgitrc.5.txt
@@ -42,6 +42,13 @@ agefile::
         hh:mm:ss". You may want to generate this file from a post-receive
         hook. Default value: "info/web/last-modified".
 
+auth-filter::
+        Specifies a command that will be invoked for authenticating repository
+        access. Receives quite a few arguments, and data on both stdin and
+        stdout for authentication processing. Details follow later in this
+        document. If no auth-filter is specified, no authentication is
+        performed. Default value: none. See also: "FILTER API".
+
 branch-sort::
         Flag which, when set to "age", enables date ordering in the branch ref
         list, and when set to "name" enables ordering by branch name. Default
@@ -605,6 +612,8 @@ specification with the relevant string; available values are:
                 URL escapes for a path and writes 'str' to the webpage.
         'html_url_arg(str)'::
                 URL escapes for an argument and writes 'str' to the webpage.
+        'html_include(file)'::
+                Includes 'file' in webpage.
 
 
 Parameters are provided to filters as follows.
@@ -635,7 +644,32 @@ source filter::
         file that is to be filtered is available on standard input and the
         filtered contents is expected on standard output.
 
-Also, all filters are handed the following environment variables:
+auth filter::
+        The authentication filter receives 11 parameters:
+          - filter action, explained below, which specifies which action the
+            filter is called for
+          - http cookie
+          - http method
+          - http referer
+          - http path
+          - http https flag
+          - cgit repo
+          - cgit page
+          - cgit url
+        When the filter action is "body", this filter must write to output the
+        HTML for displaying the login form, which POSTs to "/?p=login". When
+        the filter action is "authenticate-cookie", this filter must validate
+        the http cookie and return a 0 if it is invalid or 1 if it is invalid,
+        in the exit code / close function. If the filter action is
+        "authenticate-post", this filter receives POST'd parameters on
+        standard input, and should write to output one or more "Set-Cookie"
+        HTTP headers, each followed by a newline.
+
+        Please see `filters/simple-authentication.lua` for a clear example
+        script that may be modified.
+
+
+All filters are handed the following environment variables:
 
 - CGIT_REPO_URL (from repo.url)
 - CGIT_REPO_NAME (from repo.name)
diff --git a/filter.c b/filter.c
index 0cce7bb..a5e5e4b 100644
--- a/filter.c
+++ b/filter.c
@@ -244,6 +244,11 @@ static int html_url_arg_lua_filter(lua_State *lua_state)
         return hook_lua_filter(lua_state, html_url_arg);
 }
 
+static int html_include_lua_filter(lua_State *lua_state)
+{
+        return hook_lua_filter(lua_state, (void (*)(const char *))html_include);
+}
+
 static void cleanup_lua_filter(struct cgit_filter *base)
 {
         struct lua_filter *filter = (struct lua_filter *)base;
@@ -279,6 +284,8 @@ static int init_lua_filter(struct lua_filter *filter)
         lua_setglobal(filter->lua_state, "html_url_path");
         lua_pushcfunction(filter->lua_state, html_url_arg_lua_filter);
         lua_setglobal(filter->lua_state, "html_url_arg");
+        lua_pushcfunction(filter->lua_state, html_include_lua_filter);
+        lua_setglobal(filter->lua_state, "html_include");
 
         if (luaL_dofile(filter->lua_state, filter->script_file)) {
                 error_lua_filter(filter);
@@ -409,6 +416,10 @@ struct cgit_filter *cgit_new_filter(const char *cmd, filter_type filtertype)
                 colon = NULL;
 
         switch (filtertype) {
+                case AUTH:
+                        argument_count = 11;
+                        break;
+
                 case EMAIL:
                         argument_count = 2;
                         break;
diff --git a/filters/simple-authentication.lua b/filters/simple-authentication.lua
new file mode 100644
index 0000000..4cd4983
--- /dev/null
+++ b/filters/simple-authentication.lua
@@ -0,0 +1,225 @@
+-- This script may be used with the auth-filter. Be sure to configure it as you wish.
+--
+-- Requirements:
+--      luacrypto >= 0.3
+--      <http://mkottman.github.io/luacrypto/>
+--
+
+
+--
+--
+-- Configure these variables for your settings.
+--
+--
+
+local protected_repos = {
+        glouglou        = { laurent = true, jason = true },
+        qt              = { jason = true, bob = true }
+}
+
+local users = {
+        jason           = "secretpassword",
+        laurent         = "s3cr3t",
+        bob             = "ilikelua"
+}
+
+local secret = "BE SURE TO CUSTOMIZE THIS STRING TO SOMETHING BIG AND RANDOM"
+
+
+
+--
+--
+-- Authentication functions follow below. Swap these out if you want different authentication semantics.
+--
+--
+
+-- Sets HTTP cookie headers based on post
+function authenticate_post()
+        local password = users[post["username"]]
+        -- TODO: Implement time invariant string comparison function to mitigate against timing attack.
+        if password == nil or password ~= post["password"] then
+                construct_cookie("", "cgitauth")
+        else
+                construct_cookie(post["username"], "cgitauth")
+        end
+        return 0
+end
+
+
+-- Returns 1 if the cookie is valid and 0 if it is not.
+function authenticate_cookie()
+        accepted_users = protected_repos[cgit["repo"]]
+        if accepted_users == nil then
+                -- We return as valid if the repo is not protected.
+                return 1
+        end
+
+        local username = validate_cookie(get_cookie(http["cookie"], "cgitauth"))
+        if username == nil or not accepted_users[username] then
+                return 0
+        else
+                return 1
+        end
+end
+
+-- Prints the html for the login form.
+function body()
+        html("<h2>Authentication Required</h2>")
+        html("<form method='post' action='")
+        html_attr(cgit["login"])
+        html("'>")
+        html("<table>")
+        html("<tr><td><label for='username'>Username:</label></td><td><input id='username' name='username' autofocus /></td></tr>")
+        html("<tr><td><label for='password'>Password:</label></td><td><input id='password' name='password' type='password' /></td></tr>")
+        html("<tr><td colspan='2'><input value='Login' type='submit' /></td></tr>")
+        html("</table></form>")
+
+        return 0
+end
+
+
+--
+--
+-- Cookie construction and validation helpers.
+--
+--
+
+local crypto = require("crypto")
+