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From:
Rafael Sadowski <rafael@sizeofvoid.org>
Subject:
httpd: add custom HTTP header support #2
To:
tech@openbsd.org
Cc:
"Anthony J. Bentley" <bentley@openbsd.org>, "Kirill A. Korinsky" <kirill@korins.ky>, Stuart Henderson <stu@spacehopper.org>
Date:
Wed, 11 Feb 2026 00:59:27 +0100

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  • Rafael Sadowski:

    httpd: add custom HTTP header support #2

This is the second attempt to add custom HTTP header support to httpd.

After receiving initial feedback and advice from Stuart, I changed and
improved the whole idea (This made it very powerful but also somewhat more
complex to test) and the syntax:

Allow httpd.conf to set/add/remove custom HTTP response headers or
suppress existing ones. This enables httpd to add security headers,
custom metadata, or remove unwanted headers without modifying
app/fastcgi code.

Three new directives are added:

header set name value [always]
        Set a custom HTTP response header with the specified name
        and value.  If a header with the same name is already
        present in the response, its value will be replaced.  The
        header is added to successful responses (2xx and 3xx
        status codes) by default.

header add name value [always]
        Add a custom HTTP response header with the specified name
        and value.  Unlike set, this option appends the header
        even if one with the same name already exists, allowing
        for multiple headers with the same name.  The header is
        added to successful responses (2xx and 3xx status codes)
        by default.

header remove name
        Suppress the HTTP response header with the specified
        name.  This can be used to remove headers added by
        default, such as "Last-Modified", as well as headers
        inherited from a parent server configuration.

If always is specified, the header will be included in all
responses, including error pages (4xx and 5xx status codes).

Header names are limited to 127 characters and values to 511
characters.  Headers defined in a location block are inherited
from the server context and override defined headers with the
same name.  If you do not wish to inherit these, you can remove
them again with remove.

Example configuration:

    server "example.com" {
        listen on * tls port 443

        header add "X-Frame-Options" "SAMEORIGIN" always
        header add "X-Content-Type-Options" "nosniff" always
        header set "X-Powered-By" "OpenBSD httpd"

        location "/api/*" {
			# This location defines its own headers
			header add "Access-Control-Allow-Origin" "*"
			# Override from server context
			header set "Set-Cookie" "id=5; HttpOnly; Secure"
			# Remove from server context
			header remove "X-Frame-Options"
        }
    }

The implementation follows the existing pattern form FastCGI parameters.
So I didn't have to invent anything new. Much of the code is from
existing patterns (so the potential bugs too). Just to give one example:
The entire IMSG part.

The motivation was to have something similar to ngx_http_headers_module
without relayd coming into play. For this reason I follow the nginx pattern:

"Adds the specified field to a response header provided that the
response code equals 200, 201 (1.3.10), 204, 206, 301, 302, 303, 304,
307 (1.1.16, 1.0.13), or 308 (1.13.0). Parameter value can contain
variables."
-- https://nginx.org/en/docs/http/ngx_http_headers_module.html

I tried to test all combinations (and sure I missed some) but feel
comfortable with them. My goal was not to modify current behavior.

I would like to ask for more and more tests (big wild setups) and maybe
OKs.

Rafael

diff --git a/usr.sbin/httpd/config.c b/usr.sbin/httpd/config.c
index 300a5f2caca..5c10f4218f1 100644
--- a/usr.sbin/httpd/config.c
+++ b/usr.sbin/httpd/config.c
@@ -196,6 +196,7 @@ clear_config_server_ptrs(struct server_config *cfg)
 
 	/* clear TAILQ_HEAD */
 	memset(&cfg->fcgiparams, 0, sizeof(cfg->fcgiparams));
+	memset(&cfg->headers, 0, sizeof(cfg->headers));
 
 	/* clear TAILQ_ENTRY */
 	memset(&cfg->entry, 0, sizeof(cfg->entry));
@@ -270,7 +271,11 @@ config_setserver(struct httpd *env, struct server *srv)
 
 			/* Configure TLS if necessary. */
 			config_setserver_tls(env, srv);
-		} else {
+			/* Configure custom headers if necessary. */
+			config_setserver_headers(env, srv);
+
+		} else if (id == PROC_SERVER &&
+			   (srv->srv_conf.flags & SRVFLAG_LOCATION)) {
 			if (proc_composev(ps, id, IMSG_CFG_SERVER,
 			    iov, c) != 0) {
 				log_warn("%s: failed to compose "
@@ -278,7 +283,20 @@ config_setserver(struct httpd *env, struct server *srv)
 				    __func__, srv->srv_conf.name);
 				return (-1);
 			}
+			/* Configure FCGI parameters if necessary. */
+			config_setserver_fcgiparams(env, srv);
 
+			/* Configure custom headers if necessary. */
+			config_inherit_headers(env, srv);
+			config_setserver_headers(env, srv);
+		} else {
+			if (proc_composev(ps, id, IMSG_CFG_SERVER,
+			    iov, c) != 0) {
+				log_warn("%s: failed to compose "
+				    "IMSG_CFG_SERVER imsg for `%s'",
+				    __func__, srv->srv_conf.name);
+				return (-1);
+			}
 			/* Configure FCGI parameters if necessary. */
 			config_setserver_fcgiparams(env, srv);
 		}
@@ -442,6 +460,162 @@ config_setserver_fcgiparams(struct httpd *env, struct server *srv)
 	return (0);
 }
 
+int
+config_getserver_headers(struct httpd *env, struct imsg *imsg)
+{
+	struct server		*srv;
+	struct server_config	*srv_conf, *iconf;
+	struct custom_header	*hdr;
+	uint32_t		 id;
+	size_t			 c, nc, len;
+	uint8_t			*p = imsg->data;
+
+	len = sizeof(nc) + sizeof(id);
+	if (IMSG_DATA_SIZE(imsg) < len) {
+		log_debug("%s: invalid message length", __func__);
+		return (-1);
+	}
+
+	memcpy(&nc, p, sizeof(nc));	/* number of headers */
+	p += sizeof(nc);
+
+	memcpy(&id, p, sizeof(id));	/* server conf id */
+	srv_conf = serverconfig_byid(id);
+	p += sizeof(id);
+
+	len += nc*sizeof(*hdr);
+	if (IMSG_DATA_SIZE(imsg) < len) {
+		log_debug("%s: invalid message length", __func__);
+		return (-1);
+	}
+
+	/* Find associated server config */
+	TAILQ_FOREACH(srv, env->sc_servers, srv_entry) {
+		if (srv->srv_conf.id == id) {
+			srv_conf = &srv->srv_conf;
+			break;
+		}
+		TAILQ_FOREACH(iconf, &srv->srv_hosts, entry) {
+			if (iconf->id == id) {
+				srv_conf = iconf;
+				break;
+			}
+		}
+	}
+
+	/* Fetch custom headers */
+	for (c = 0; c < nc; c++) {
+		if ((hdr = calloc(1, sizeof(*hdr))) == NULL)
+			fatalx("headers out of memory");
+		memcpy(hdr, p, sizeof(*hdr));
+		TAILQ_INSERT_HEAD(&srv_conf->headers, hdr, entry);
+
+		p += sizeof(*hdr);
+	}
+
+	return (0);
+}
+
+static int
+header_exists(struct server_config *srv_conf, const char *name)
+{
+	struct custom_header	*hdr;
+
+	TAILQ_FOREACH(hdr, &srv_conf->headers, entry) {
+		if (strcasecmp(hdr->name, name) == 0)
+			return (1);
+	}
+	return (0);
+}
+
+/*
+ * Inherit headers from parent server, skipping those
+ * already defined in the location.
+ */
+void
+config_inherit_headers(struct httpd *env, struct server *srv)
+{
+	struct server		*parent_srv;
+	struct server_config	*srv_conf = &srv->srv_conf;
+	struct custom_header	*hdr, *hdr_copy;
+
+	if (!(srv_conf->flags & SRVFLAG_LOCATION))
+		return;
+
+	/* Find parent server by parent_id */
+	TAILQ_FOREACH(parent_srv, env->sc_servers, srv_entry) {
+		if (parent_srv->srv_conf.id == srv_conf->parent_id)
+			break;
+	}
+
+	if (parent_srv == NULL)
+		return;
+
+	TAILQ_FOREACH(hdr, &parent_srv->srv_conf.headers, entry) {
+		if (header_exists(srv_conf, hdr->name)) {
+			DPRINTF("%s: skipping header \"%s\" from parent "
+			    "\"%s\", overridden in location \"%s\"",
+			    __func__, hdr->name,
+			    parent_srv->srv_conf.name, srv_conf->location);
+			continue;
+		}
+
+		if ((hdr_copy = calloc(1, sizeof(*hdr_copy))) == NULL)
+			fatal("out of memory");
+
+		strlcpy(hdr_copy->name, hdr->name, sizeof(hdr_copy->name));
+		strlcpy(hdr_copy->value, hdr->value, sizeof(hdr_copy->value));
+		hdr_copy->flags = hdr->flags;
+
+		TAILQ_INSERT_TAIL(&srv_conf->headers, hdr_copy, entry);
+		DPRINTF("%s: inheriting header \"%s\" from parent \"%s\" "
+		    "to location \"%s\"", __func__, hdr->name,
+		    parent_srv->srv_conf.name, srv_conf->location);
+	}
+}
+
+int
+config_setserver_headers(struct httpd *env, struct server *srv)
+{
+	struct privsep		*ps = env->sc_ps;
+	struct server_config	*srv_conf = &srv->srv_conf;
+	struct custom_header	*hdr;
+	struct iovec		*iov;
+	size_t			 c = 0, nc = 0;
+
+	DPRINTF("%s: sending headers for \"%s[%u]\" to %s fd %d", __func__,
+	    srv_conf->name, srv_conf->id, ps->ps_title[PROC_SERVER],
+	    srv->srv_s);
+
+	if (TAILQ_EMPTY(&srv_conf->headers))	/* nothing to do */
+		return (0);
+
+	TAILQ_FOREACH(hdr, &srv_conf->headers, entry) {
+		nc++;
+	}
+	if ((iov = calloc(nc + 2, sizeof(*iov))) == NULL)
+		return (-1);
+
+	iov[c].iov_base = &nc;			/* number of headers */
+	iov[c++].iov_len = sizeof(nc);
+	iov[c].iov_base = &srv_conf->id;	/* server config id */
+	iov[c++].iov_len = sizeof(srv_conf->id);
+
+	TAILQ_FOREACH(hdr, &srv_conf->headers, entry) {	/* push headers */
+		iov[c].iov_base = hdr;
+		iov[c++].iov_len = sizeof(*hdr);
+	}
+	if (proc_composev(ps, PROC_SERVER, IMSG_CFG_HEADERS, iov, c) != 0) {
+		log_warn("%s: failed to compose IMSG_CFG_HEADERS imsg for "
+		    "`%s'", __func__, srv_conf->name);
+		free(iov);
+		return (-1);
+	}
+	free(iov);
+
+	return (0);
+}
+
 int
 config_setserver_tls(struct httpd *env, struct server *srv)
 {
diff --git a/usr.sbin/httpd/httpd.conf.5 b/usr.sbin/httpd/httpd.conf.5
index 3053709a359..72d80628ac6 100644
--- a/usr.sbin/httpd/httpd.conf.5
+++ b/usr.sbin/httpd/httpd.conf.5
@@ -464,6 +464,57 @@ Enable static gzip compression to save bandwidth.
 If gzip encoding is accepted and if the requested file exists with
 an additional .gz suffix, use the compressed file instead and deliver
 it with content encoding gzip.
+.It Ic header Ar option
+Manipulate HTTP response headers.
+Multiple
+.Ic header
+statements may be specified.
+Valid options are:
+.Bl -tag -width Ds
+.It Ic set Ar name Ar value Op Ic always
+Set a custom HTTP response header with the specified
+.Ar name
+and
+.Ar value .
+If a header with the same
+.Ar name
+is already present in the response, its value will be replaced.
+The header is added to successful responses
+(2xx and 3xx status codes) by default.
+.It Ic add Ar name Ar value Op Ic always
+Add a custom HTTP response header with the specified
+.Ar name
+and
+.Ar value .
+Unlike
+.Ic set ,
+this option appends the header even if one with the same
+.Ar name
+already exists, allowing for multiple headers with the same name.
+The header is added to successful responses
+(2xx and 3xx status codes) by default.
+.It Ic remove Ar name
+Suppress the HTTP response header with the specified
+.Ar name .
+This can be used to remove headers added by default, such as
+.Qq Last-Modified ,
+as well as headers inherited from a parent server configuration.
+.El
+.Pp
+If
+.Ic always
+is specified, the header will be included in all responses,
+including error pages (4xx and 5xx status codes).
+.Pp
+Header names are limited to 127 characters and values to 511 characters.
+Headers defined in a
+.Ic location
+block are inherited from the
+.Ic server
+context and override defined headers with the same name.
+If you do not wish to inherit these, you can remove them again with
+.Ic remove .
+
 .It Ic hsts Oo Ar option Oc
 Enable HTTP Strict Transport Security.
 Valid options are:
@@ -895,6 +946,32 @@ server "example.com" {
 	}
 }
 .Ed
+.Pp
+Custom HTTP headers can be added to responses for security or compatibility:
+.Bd -literal -offset indent
+server "example.com" {
+	listen on * tls port 443
+
+	header set "X-Powered-By" "OpenBSD httpd"
+
+	header set "X-Content-Type-Options" "nosniff" always
+	header set "X-Frame-Options" "DENY" always
+
+	header add "Set-Cookie" "id=23; HttpOnly; Secure"
+
+	# Remove default Last-Modified header
+	header remove "Last-Modified"
+
+	location "/api/*" {
+		# This location defines its own headers
+		header add "Access-Control-Allow-Origin" "*"
+		# Override from server context
+		header set "Set-Cookie" "id=5; HttpOnly; Secure"
+		# Remove from server context
+		header remove "X-Frame-Options"
+	}
+}
+.Ed
 .Sh SEE ALSO
 .Xr htpasswd 1 ,
 .Xr glob 7 ,
diff --git a/usr.sbin/httpd/httpd.h b/usr.sbin/httpd/httpd.h
index baf11d1b523..096f68f02b0 100644
--- a/usr.sbin/httpd/httpd.h
+++ b/usr.sbin/httpd/httpd.h
@@ -209,6 +209,7 @@ enum imsg_type {
 	IMSG_CFG_MEDIA,
 	IMSG_CFG_AUTH,
 	IMSG_CFG_FCGI,
+	IMSG_CFG_HEADERS,
 	IMSG_CFG_DONE,
 	IMSG_LOG_ACCESS,
 	IMSG_LOG_ERROR,
@@ -470,6 +471,19 @@ struct fastcgi_param {
 };
 TAILQ_HEAD(server_fcgiparams, fastcgi_param);
 
+struct custom_header {
+	char			name[128];
+	char			value[512];
+	uint8_t			flags;
+#define HEADER_REMOVE		0x01
+#define HEADER_ADD		0x02
+#define HEADER_SET		0x04
+#define HEADER_ALWAYS		0x08
+
+	TAILQ_ENTRY(custom_header) entry;
+};
+TAILQ_HEAD(server_headers, custom_header);
+
 struct server_config {
 	uint32_t		 id;
 	uint32_t		 parent_id;
@@ -540,6 +554,7 @@ struct server_config {
 
 	struct server_fcgiparams fcgiparams;
 	int			 fcgistrip;
+	struct server_headers	 headers;
 	char			 errdocroot[HTTPD_ERRDOCROOT_MAX];
 
 	TAILQ_ENTRY(server_config) entry;
@@ -673,6 +688,8 @@ void	 server_http(void);
 int	 server_httpdesc_init(struct client *);
 void	 server_read_http(struct bufferevent *, void *);
 void	 server_abort_http(struct client *, unsigned int, const char *);
+void	 server_custom_headers(struct server_config *, struct kvtree *,
+	    unsigned int);
 unsigned int
 	 server_httpmethod_byname(const char *);
 const char
@@ -825,9 +842,12 @@ int	 config_getcfg(struct httpd *, struct imsg *);
 int	 config_setserver(struct httpd *, struct server *);
 int	 config_setserver_tls(struct httpd *, struct server *);
 int	 config_setserver_fcgiparams(struct httpd *, struct server *);
+int	 config_setserver_headers(struct httpd *, struct server *);
+void	 config_inherit_headers(struct httpd *, struct server *);
 int	 config_getserver(struct httpd *, struct imsg *);
 int	 config_getserver_tls(struct httpd *, struct imsg *);
 int	 config_getserver_fcgiparams(struct httpd *, struct imsg *);
+int	 config_getserver_headers(struct httpd *, struct imsg *);
 int	 config_setmedia(struct httpd *, struct media_type *);
 int	 config_getmedia(struct httpd *, struct imsg *);
 int	 config_setauth(struct httpd *, struct auth *);
diff --git a/usr.sbin/httpd/parse.y b/usr.sbin/httpd/parse.y
index 326b249662f..d2d6282439f 100644
--- a/usr.sbin/httpd/parse.y
+++ b/usr.sbin/httpd/parse.y
@@ -142,6 +142,7 @@ typedef struct {
 %token	ERROR INCLUDE AUTHENTICATE WITH BLOCK DROP RETURN PASS REWRITE
 %token	CA CLIENT CRL OPTIONAL PARAM FORWARDED FOUND NOT
 %token	ERRDOCS GZIPSTATIC BANNER
+%token	HEADER ADD ALWAYS REMOVE SET
 %token	<v.string>	STRING
 %token  <v.number>	NUMBER
 %type	<v.port>	port
@@ -323,6 +324,7 @@ server		: SERVER optmatch STRING	{
 			SPLAY_INIT(&srv->srv_clients);
 			TAILQ_INIT(&srv->srv_hosts);
 			TAILQ_INIT(&srv_conf->fcgiparams);
+			TAILQ_INIT(&srv_conf->headers);
 
 			TAILQ_INSERT_TAIL(&srv->srv_hosts, srv_conf, entry);
 		} '{' optnl serveropts_l '}'	{
@@ -557,6 +559,7 @@ serveroptsl	: LISTEN ON STRING opttls port	{
 		| root
 		| directory
 		| banner
+		| header
 		| logformat
 		| fastcgi
 		| authenticate
@@ -643,6 +646,7 @@ serveroptsl	: LISTEN ON STRING opttls port	{
 			srv = s;
 			srv_conf = &srv->srv_conf;
 			SPLAY_INIT(&srv->srv_clients);
+			TAILQ_INIT(&srv_conf->headers);
 		} '{' optnl serveropts_l '}'	{
 			struct server	*s = NULL;
 			uint32_t	 f;
@@ -710,6 +714,147 @@ banner		: BANNER		{
 		}
 		;
 
+header		: HEADER REMOVE STRING	{
+			struct custom_header	*hdr;
+
+			if ((hdr = calloc(1, sizeof(*hdr))) == NULL)
+				fatal("out of memory");
+
+			if (strlcpy(hdr->name, $3, sizeof(hdr->name)) >=
+			    sizeof(hdr->name)) {
+				yyerror("header name truncated");
+				free($3);
+				free(hdr);
+				YYERROR;
+			}
+			if (strcmp("Server", hdr->name) == 0) {
+				yyerror("'header remover Server' "
+					"ignored, use 'no banner'");
+				free($3);
+				free(hdr);
+				YYERROR;
+			}
+			free($3);
+
+			hdr->flags = HEADER_REMOVE;
+			TAILQ_INSERT_TAIL(&srv->srv_conf.headers, hdr, entry);
+		}
+		| HEADER ADD STRING STRING	{
+			struct custom_header	*hdr;
+
+			if ((hdr = calloc(1, sizeof(*hdr))) == NULL)
+				fatal("out of memory");
+
+			if (strlcpy(hdr->name, $3, sizeof(hdr->name)) >=
+			    sizeof(hdr->name)) {
+				yyerror("header name truncated");
+				free($3);
+				free($4);
+				free(hdr);
+				YYERROR;
+			}
+			free($3);
+
+			if (strlcpy(hdr->value, $4, sizeof(hdr->value)) >=
+			    sizeof(hdr->value)) {
+				yyerror("header value truncated");
+				free($4);
+				free(hdr);
+				YYERROR;
+			}
+			free($4);
+
+			hdr->flags = HEADER_ADD;
+			TAILQ_INSERT_TAIL(&srv->srv_conf.headers, hdr, entry);
+		}
+		| HEADER ADD STRING STRING ALWAYS	{
+			struct custom_header	*hdr;
+
+			if ((hdr = calloc(1, sizeof(*hdr))) == NULL)
+				fatal("out of memory");
+
+			if (strlcpy(hdr->name, $3, sizeof(hdr->name)) >=
+			    sizeof(hdr->name)) {
+				yyerror("header name truncated");
+				free($3);
+				free($4);
+				free(hdr);
+				YYERROR;
+			}
+			free($3);
+
+			if (strlcpy(hdr->value, $4, sizeof(hdr->value)) >=
+			    sizeof(hdr->value)) {
+				yyerror("header value truncated");
+				free($4);
+				free(hdr);
+				YYERROR;
+			}
+			free($4);
+
+			hdr->flags = HEADER_ADD;
+			hdr->flags |= HEADER_ALWAYS;
+			TAILQ_INSERT_TAIL(&srv->srv_conf.headers, hdr, entry);
+		}
+		| HEADER SET STRING STRING	{
+			struct custom_header	*hdr;
+
+			if ((hdr = calloc(1, sizeof(*hdr))) == NULL)
+				fatal("out of memory");
+
+			if (strlcpy(hdr->name, $3, sizeof(hdr->name)) >=
+			    sizeof(hdr->name)) {
+				yyerror("header name truncated");
+				free($3);
+				free($4);
+				free(hdr);
+				YYERROR;
+			}
+			free($3);
+
+			if (strlcpy(hdr->value, $4, sizeof(hdr->value)) >=
+			    sizeof(hdr->value)) {
+				yyerror("header value truncated");
+				free($4);
+				free(hdr);
+				YYERROR;
+			}
+			free($4);
+
+			hdr->flags = HEADER_SET;
+			TAILQ_INSERT_TAIL(&srv->srv_conf.headers, hdr, entry);
+		}
+		| HEADER SET STRING STRING ALWAYS	{
+			struct custom_header	*hdr;
+
+			if ((hdr = calloc(1, sizeof(*hdr))) == NULL)
+				fatal("out of memory");
+
+			if (strlcpy(hdr->name, $3, sizeof(hdr->name)) >=
+			    sizeof(hdr->name)) {
+				yyerror("header name truncated");
+				free($3);
+				free($4);
+				free(hdr);
+				YYERROR;
+			}
+			free($3);
+
+			if (strlcpy(hdr->value, $4, sizeof(hdr->value)) >=
+			    sizeof(hdr->value)) {
+				yyerror("header value truncated");
+				free($4);
+				free(hdr);
+				YYERROR;
+			}
+			free($4);
+
+			hdr->flags = HEADER_SET;
+			hdr->flags |= HEADER_ALWAYS;
+			TAILQ_INSERT_TAIL(&srv->srv_conf.headers, hdr, entry);
+		}
+		;
+
 optfound	: /* empty */	{ $$ = 0; }
 		| FOUND		{ $$ = 1; }
 		| NOT FOUND	{ $$ = -1; }
@@ -1447,7 +1592,9 @@ lookup(char *s)
 	/* this has to be sorted always */
 	static const struct keywords keywords[] = {
 		{ "access",		ACCESS },
+		{ "add",		ADD },
 		{ "alias",		ALIAS },
+		{ "always",		ALWAYS },
 		{ "authenticate",	AUTHENTICATE},
 		{ "auto",		AUTO },
 		{ "backlog",		BACKLOG },
@@ -1475,6 +1622,7 @@ lookup(char *s)
 		{ "forwarded",		FORWARDED },
 		{ "found",		FOUND },
 		{ "gzip-static",	GZIPSTATIC },
+		{ "header",		HEADER },
 		{ "hsts",		HSTS },
 		{ "include",		INCLUDE },
 		{ "index",		INDEX },
@@ -1500,6 +1648,7 @@ lookup(char *s)
 		{ "prefork",		PREFORK },
 		{ "preload",		PRELOAD },
 		{ "protocols",		PROTOCOLS },
+		{ "remove",		REMOVE },
 		{ "request",		REQUEST },
 		{ "requests",		REQUESTS },
 		{ "return",		RETURN },
@@ -1507,6 +1656,7 @@ lookup(char *s)
 		{ "root",		ROOT },
 		{ "sack",		SACK },
 		{ "server",		SERVER },
+		{ "set",		SET },
 		{ "socket",		SOCKET },
 		{ "strip",		STRIP },
 		{ "style",		STYLE },
@@ -2298,12 +2448,24 @@ server_inherit(struct server *src, struct server_config *alias,
     struct server_config *addr)
 {
 	struct server	*dst, *s, *dstl;
+	struct custom_header	*hdr, *nhdr;
 
 	if ((dst = calloc(1, sizeof(*dst))) == NULL)
 		fatal("out of memory");
 
 	/* Copy the source server and assign a new Id */
 	memcpy(&dst->srv_conf, &src->srv_conf, sizeof(dst->srv_conf));
+
+	TAILQ_INIT(&dst->srv_conf.headers);
+	TAILQ_FOREACH(hdr, &src->srv_conf.headers, entry) {
+		if ((nhdr = calloc(1, sizeof(*nhdr))) == NULL)
+			fatal("out of memory");
+		strlcpy(nhdr->name, hdr->name, sizeof(nhdr->name));
+		strlcpy(nhdr->value, hdr->value, sizeof(nhdr->value));
+		nhdr->flags = hdr->flags;
+		TAILQ_INSERT_TAIL(&dst->srv_conf.headers, nhdr, entry);
+	}
+
 	if ((dst->srv_conf.tls_cert_file =
 	    strdup(src->srv_conf.tls_cert_file)) == NULL)
 		fatal("out of memory");
@@ -2393,6 +2555,18 @@ server_inherit(struct server *src, struct server_config *alias,
 			fatal("out of memory");
 
 		memcpy(&dstl->srv_conf, &s->srv_conf, sizeof(dstl->srv_conf));
+
+		/* Copy custom headers from source location */
+		TAILQ_INIT(&dstl->srv_conf.headers);
+		TAILQ_FOREACH(hdr, &s->srv_conf.headers, entry) {
+			if ((nhdr = calloc(1, sizeof(*nhdr))) == NULL)
+				fatal("out of memory");
+			strlcpy(nhdr->name, hdr->name, sizeof(nhdr->name));
+			strlcpy(nhdr->value, hdr->value, sizeof(nhdr->value));
+			nhdr->flags = hdr->flags;
+			TAILQ_INSERT_TAIL(&dstl->srv_conf.headers, nhdr, entry);
+		}
+
 		strlcpy(dstl->srv_conf.name, alias->name,
 		    sizeof(dstl->srv_conf.name));
 
diff --git a/usr.sbin/httpd/server.c b/usr.sbin/httpd/server.c
index a38cf018d81..ed97f3f7e3c 100644
--- a/usr.sbin/httpd/server.c
+++ b/usr.sbin/httpd/server.c
@@ -470,6 +470,7 @@ void
 serverconfig_free(struct server_config *srv_conf)
 {
 	struct fastcgi_param	*param, *tparam;
+	struct custom_header	*hdr, *thdr;
 
 	free(srv_conf->return_uri);
 	free(srv_conf->tls_ca_file);
@@ -485,6 +486,9 @@ serverconfig_free(struct server_config *srv_conf)
 
 	TAILQ_FOREACH_SAFE(param, &srv_conf->fcgiparams, entry, tparam)
 		free(param);
+
+	TAILQ_FOREACH_SAFE(hdr, &srv_conf->headers, entry, thdr)
+		free(hdr);
 }
 
 void
@@ -503,6 +507,7 @@ serverconfig_reset(struct server_config *srv_conf)
 	srv_conf->tls_ocsp_staple = NULL;
 	srv_conf->tls_ocsp_staple_file = NULL;
 	TAILQ_INIT(&srv_conf->fcgiparams);
+	TAILQ_INIT(&srv_conf->headers);
 }
 
 struct server *
@@ -1366,6 +1371,9 @@ server_dispatch_parent(int fd, struct privsep_proc *p, struct imsg *imsg)
 	case IMSG_CFG_FCGI:
 		config_getserver_fcgiparams(httpd_env, imsg);
 		break;
+	case IMSG_CFG_HEADERS:
+		config_getserver_headers(httpd_env, imsg);
+		break;
 	case IMSG_CFG_DONE:
 		config_getcfg(httpd_env, imsg);
 		break;
diff --git a/usr.sbin/httpd/server_fcgi.c b/usr.sbin/httpd/server_fcgi.c
index c5f9917204c..02165ba3e32 100644
--- a/usr.sbin/httpd/server_fcgi.c
+++ b/usr.sbin/httpd/server_fcgi.c
@@ -723,6 +723,8 @@ server_fcgi_header(struct client *clt, unsigned int code)
 			return (-1);
 	}
 
+	server_custom_headers(srv_conf, &resp->http_headers, code);
+
 	/* Date header is mandatory and should be added as late as possible */
 	key.kv_key = "Date";
 	if (kv_find(&resp->http_headers, &key) == NULL &&
diff --git a/usr.sbin/httpd/server_http.c b/usr.sbin/httpd/server_http.c
index afdb73f243f..96faa0fb4e5 100644
--- a/usr.sbin/httpd/server_http.c
+++ b/usr.sbin/httpd/server_http.c
@@ -50,10 +50,12 @@ void		 server_httpdesc_free(struct http_descriptor *);
 int		 server_http_authenticate(struct server_config *,
 		    struct client *);
 static int	 http_version_num(char *);
+static int	 http_is_success(unsigned int code);
 char		*server_expand_http(struct client *, const char *,
 		    char *, size_t);
 char		*replace_var(char *, const char *, const char *);
 char		*read_errdoc(const char *, const char *);
+char		*get_always_custom_headers(struct server_config *);
 
 static struct http_method	 http_methods[] = HTTP_METHODS;
 static struct http_error	 http_errors[] = HTTP_ERRORS;
@@ -219,6 +221,25 @@ http_version_num(char *version)
 	}
 	return (0);
 }
+static int
+http_is_success(unsigned int code)
+{
+	switch (code) {
+	case 200:
+	case 201:
+	case 204:
+	case 206:
+	case 301:
+	case 302:
+	case 303:
+	case 304:
+	case 307:
+	case 308:
+		return (0);
+	default:
+		return (1);
+	}
+}
 
 void
 server_read_http(struct bufferevent *bev, void *arg)
@@ -892,6 +913,7 @@ server_abort_http(struct client *clt, unsigned int code, const char *msg)
 	char			 tmbuf[32], hbuf[128], *hstsheader = NULL;
 	char			*clenheader = NULL;
 	char			*bannerheader = NULL, *bannertoken = NULL;
+	char			*customheaders = NULL;
 	char			 buf[IBUF_READ_SIZE];
 	char			*escapedmsg = NULL;
 	char			 cstr[5];
@@ -1060,6 +1082,8 @@ server_abort_http(struct client *clt, unsigned int code, const char *msg)
 			goto done;
 		}
 
+	customheaders = get_always_custom_headers(srv_conf);
+
 	/* Add basic HTTP headers */
 	if (asprintf(&httpmsg,
 	    "HTTP/1.0 %03d %s\r\n"
@@ -1070,6 +1094,7 @@ server_abort_http(struct client *clt, unsigned int code, const char *msg)
 	    "%s"
 	    "%s"
 	    "%s"
+	    "%s"
 	    "\r\n"
 	    "%s",
 	    code, httperr, tmbuf,
@@ -1077,6 +1102,7 @@ server_abort_http(struct client *clt, unsigned int code, const char *msg)
 	    clenheader == NULL ? "" : clenheader,
 	    extraheader == NULL ? "" : extraheader,
 	    hstsheader == NULL ? "" : hstsheader,
+	    customheaders == NULL ? "" : customheaders,
 	    desc->http_method == HTTP_METHOD_HEAD || clenheader == NULL ?
 	    "" : body) == -1)
 		goto done;
@@ -1092,6 +1118,7 @@ server_abort_http(struct client *clt, unsigned int code, const char *msg)
 	free(clenheader);
 	free(bannerheader);
 	free(bannertoken);
+	free(customheaders);
 	if (msg == NULL)
 		msg = "\"\"";
 	if (asprintf(&httpmsg, "%s (%03d %s)", msg, code, httperr) == -1) {
@@ -1561,6 +1588,73 @@ server_locationaccesstest(struct server_config *srv_conf, const char *path)
 	    (ret == 0 && SRVFLAG_LOCATION_NOT_FOUND & srv_conf->flags));
 }
 
+void
+server_custom_headers(struct server_config *srv_conf, struct kvtree *headers,
+    unsigned int code)
+{
+	struct custom_header	*hdr;
+	struct kv		*kv, search;
+
+	TAILQ_FOREACH(hdr, &srv_conf->headers, entry) {
+		/* Only include headers not marked ALWAYS on success. */
+		if (!(hdr->flags & HEADER_ALWAYS) &&
+		    http_is_success(code) != 0)
+			continue;
+
+		search.kv_key = hdr->name;
+
+		/* deletes all existing headers of the same key */
+		if (hdr->flags & HEADER_REMOVE) {
+			while ((kv = kv_find(headers, &search)) != NULL)
+				kv_delete(headers, kv);
+		/* replaces all existing headers of the same name */
+		} else if (hdr->flags & HEADER_SET) {
+			while ((kv = kv_find(headers, &search)) != NULL)
+				kv_delete(headers, kv);
+
+			if (kv_add(headers, hdr->name, hdr->value) == NULL)
+				return;
+		/* appends a new header without checking for duplicates */
+		} else if (hdr->flags & HEADER_ADD) {
+			if (kv_add(headers, hdr->name, hdr->value) == NULL)
+				return;
+		}
+	}
+}
+
+/*
+ * Build a raw custom HTTP header that only includes headers marked as always
+ */
+char *
+get_always_custom_headers(struct server_config *srv_conf)
+{
+	struct custom_header *hdr;
+	char *headers = NULL;
+	char *tmp = NULL;
+
+	TAILQ_FOREACH(hdr, &srv_conf->headers, entry) {
+		if (!(hdr->flags & HEADER_ALWAYS)
+		      || hdr->flags & HEADER_REMOVE)
+			continue;
+
+		if (headers == NULL) {
+			if (asprintf(&headers, "%s: %s\r\n", hdr->name,
+			    hdr->value) == -1) {
+				return (NULL);
+			}
+		} else {
+			if (asprintf(&tmp, "%s%s: %s\r\n", headers, hdr->name,
+			    hdr->value) == -1) {
+				free(headers);
+				return (NULL);
+			}
+			free(headers);
+			headers = tmp;
+		}
+	}
+	return (headers);
+}
+
 int
 server_response_http(struct client *clt, unsigned int code,
     struct media_type *media, off_t size, time_t mtime)
@@ -1627,6 +1721,7 @@ server_response_http(struct client *clt, unsigned int code,
 		    "; preload" : "") == -1)
 			return (-1);
 	}
+	server_custom_headers(srv_conf, &resp->http_headers, code);
 
 	/* Date header is mandatory and should be added as late as possible */
 	if (server_http_time(time(NULL), tmbuf, sizeof(tmbuf)) <= 0 ||