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Edit File: ngx_mail_ssl_module.c

/*
 * Copyright (C) Igor Sysoev
 * Copyright (C) Nginx, Inc.
 */

#include <ngx_config.h>
#include <ngx_core.h>
#include <ngx_mail.h>

#define NGX_DEFAULT_CIPHERS     "HIGH:!aNULL:!MD5"
#define NGX_DEFAULT_ECDH_CURVE  "auto"

#ifdef TLSEXT_TYPE_application_layer_protocol_negotiation
static int ngx_mail_ssl_alpn_select(ngx_ssl_conn_t *ssl_conn,
    const unsigned char **out, unsigned char *outlen,
    const unsigned char *in, unsigned int inlen, void *arg);
#endif

static void *ngx_mail_ssl_create_conf(ngx_conf_t *cf);
static char *ngx_mail_ssl_merge_conf(ngx_conf_t *cf, void *parent, void *child);

static char *ngx_mail_ssl_starttls(ngx_conf_t *cf, ngx_command_t *cmd,
    void *conf);
static char *ngx_mail_ssl_password_file(ngx_conf_t *cf, ngx_command_t *cmd,
    void *conf);
static char *ngx_mail_ssl_session_cache(ngx_conf_t *cf, ngx_command_t *cmd,
    void *conf);

static char *ngx_mail_ssl_conf_command_check(ngx_conf_t *cf, void *post,
    void *data);

static ngx_conf_enum_t  ngx_mail_starttls_state[] = {
    { ngx_string("off"), NGX_MAIL_STARTTLS_OFF },
    { ngx_string("on"), NGX_MAIL_STARTTLS_ON },
    { ngx_string("only"), NGX_MAIL_STARTTLS_ONLY },
    { ngx_null_string, 0 }
};

static ngx_conf_bitmask_t  ngx_mail_ssl_protocols[] = {
    { ngx_string("SSLv2"), NGX_SSL_SSLv2 },
    { ngx_string("SSLv3"), NGX_SSL_SSLv3 },
    { ngx_string("TLSv1"), NGX_SSL_TLSv1 },
    { ngx_string("TLSv1.1"), NGX_SSL_TLSv1_1 },
    { ngx_string("TLSv1.2"), NGX_SSL_TLSv1_2 },
    { ngx_string("TLSv1.3"), NGX_SSL_TLSv1_3 },
    { ngx_null_string, 0 }
};

static ngx_conf_enum_t  ngx_mail_ssl_verify[] = {
    { ngx_string("off"), 0 },
    { ngx_string("on"), 1 },
    { ngx_string("optional"), 2 },
    { ngx_string("optional_no_ca"), 3 },
    { ngx_null_string, 0 }
};

static ngx_conf_post_t  ngx_mail_ssl_conf_command_post =
    { ngx_mail_ssl_conf_command_check };

static ngx_command_t  ngx_mail_ssl_commands[] = {

{ ngx_string("starttls"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_mail_ssl_starttls,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, starttls),
      ngx_mail_starttls_state },

{ ngx_string("ssl_certificate"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_array_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, certificates),
      NULL },

{ ngx_string("ssl_certificate_key"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_array_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, certificate_keys),
      NULL },

{ ngx_string("ssl_password_file"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_mail_ssl_password_file,
      NGX_MAIL_SRV_CONF_OFFSET,
      0,
      NULL },

{ ngx_string("ssl_dhparam"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, dhparam),
      NULL },

{ ngx_string("ssl_ecdh_curve"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, ecdh_curve),
      NULL },

{ ngx_string("ssl_protocols"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_1MORE,
      ngx_conf_set_bitmask_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, protocols),
      &ngx_mail_ssl_protocols },

{ ngx_string("ssl_ciphers"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, ciphers),
      NULL },

{ ngx_string("ssl_prefer_server_ciphers"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_FLAG,
      ngx_conf_set_flag_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, prefer_server_ciphers),
      NULL },

{ ngx_string("ssl_session_cache"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE12,
      ngx_mail_ssl_session_cache,
      NGX_MAIL_SRV_CONF_OFFSET,
      0,
      NULL },

{ ngx_string("ssl_session_tickets"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_FLAG,
      ngx_conf_set_flag_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, session_tickets),
      NULL },

{ ngx_string("ssl_session_ticket_key"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_array_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, session_ticket_keys),
      NULL },

{ ngx_string("ssl_session_timeout"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_sec_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, session_timeout),
      NULL },

{ ngx_string("ssl_verify_client"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_enum_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, verify),
      &ngx_mail_ssl_verify },

{ ngx_string("ssl_verify_depth"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_num_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, verify_depth),
      NULL },

{ ngx_string("ssl_client_certificate"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, client_certificate),
      NULL },

{ ngx_string("ssl_trusted_certificate"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, trusted_certificate),
      NULL },

{ ngx_string("ssl_crl"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, crl),
      NULL },

{ ngx_string("ssl_conf_command"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE2,
      ngx_conf_set_keyval_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, conf_commands),
      &ngx_mail_ssl_conf_command_post },

ngx_null_command
};

static ngx_mail_module_t  ngx_mail_ssl_module_ctx = {
    NULL,                                  /* protocol */

NULL,                                  /* create main configuration */
    NULL,                                  /* init main configuration */

ngx_mail_ssl_create_conf,              /* create server configuration */
    ngx_mail_ssl_merge_conf                /* merge server configuration */
};

ngx_module_t  ngx_mail_ssl_module = {
    NGX_MODULE_V1,
    &ngx_mail_ssl_module_ctx,              /* module context */
    ngx_mail_ssl_commands,                 /* module directives */
    NGX_MAIL_MODULE,                       /* module type */
    NULL,                                  /* init master */
    NULL,                                  /* init module */
    NULL,                                  /* init process */
    NULL,                                  /* init thread */
    NULL,                                  /* exit thread */
    NULL,                                  /* exit process */
    NULL,                                  /* exit master */
    NGX_MODULE_V1_PADDING
};

static ngx_str_t ngx_mail_ssl_sess_id_ctx = ngx_string("MAIL");

#ifdef TLSEXT_TYPE_application_layer_protocol_negotiation

static int
ngx_mail_ssl_alpn_select(ngx_ssl_conn_t *ssl_conn, const unsigned char **out,
    unsigned char *outlen, const unsigned char *in, unsigned int inlen,
    void *arg)
{
    unsigned int               srvlen;
    unsigned char             *srv;
    ngx_connection_t          *c;
    ngx_mail_session_t        *s;
    ngx_mail_core_srv_conf_t  *cscf;
#if (NGX_DEBUG)
    unsigned int               i;
#endif

c = ngx_ssl_get_connection(ssl_conn);
    s = c->data;

#if (NGX_DEBUG)
    for (i = 0; i < inlen; i += in[i] + 1) {
        ngx_log_debug2(NGX_LOG_DEBUG_MAIL, c->log, 0,
                       "SSL ALPN supported by client: %*s",
                       (size_t) in[i], &in[i + 1]);
    }
#endif

cscf = ngx_mail_get_module_srv_conf(s, ngx_mail_core_module);

srv = cscf->protocol->alpn.data;
    srvlen = cscf->protocol->alpn.len;

if (SSL_select_next_proto((unsigned char **) out, outlen, srv, srvlen,
                              in, inlen)
        != OPENSSL_NPN_NEGOTIATED)
    {
        return SSL_TLSEXT_ERR_ALERT_FATAL;
    }

ngx_log_debug2(NGX_LOG_DEBUG_MAIL, c->log, 0,
                   "SSL ALPN selected: %*s", (size_t) *outlen, *out);

return SSL_TLSEXT_ERR_OK;
}

#endif

static void *
ngx_mail_ssl_create_conf(ngx_conf_t *cf)
{
    ngx_mail_ssl_conf_t  *scf;

scf = ngx_pcalloc(cf->pool, sizeof(ngx_mail_ssl_conf_t));
    if (scf == NULL) {
        return NULL;
    }

/*
     * set by ngx_pcalloc():
     *
     *     scf->listen = 0;
     *     scf->protocols = 0;
     *     scf->dhparam = { 0, NULL };
     *     scf->ecdh_curve = { 0, NULL };
     *     scf->client_certificate = { 0, NULL };
     *     scf->trusted_certificate = { 0, NULL };
     *     scf->crl = { 0, NULL };
     *     scf->ciphers = { 0, NULL };
     *     scf->shm_zone = NULL;
     */

scf->starttls = NGX_CONF_UNSET_UINT;
    scf->certificates = NGX_CONF_UNSET_PTR;
    scf->certificate_keys = NGX_CONF_UNSET_PTR;
    scf->passwords = NGX_CONF_UNSET_PTR;
    scf->conf_commands = NGX_CONF_UNSET_PTR;
    scf->prefer_server_ciphers = NGX_CONF_UNSET;
    scf->verify = NGX_CONF_UNSET_UINT;
    scf->verify_depth = NGX_CONF_UNSET_UINT;
    scf->builtin_session_cache = NGX_CONF_UNSET;
    scf->session_timeout = NGX_CONF_UNSET;
    scf->session_tickets = NGX_CONF_UNSET;
    scf->session_ticket_keys = NGX_CONF_UNSET_PTR;

return scf;
}

static char *
ngx_mail_ssl_merge_conf(ngx_conf_t *cf, void *parent, void *child)
{
    ngx_mail_ssl_conf_t *prev = parent;
    ngx_mail_ssl_conf_t *conf = child;

char                *mode;
    ngx_pool_cleanup_t  *cln;

ngx_conf_merge_uint_value(conf->starttls, prev->starttls,
                         NGX_MAIL_STARTTLS_OFF);

ngx_conf_merge_value(conf->session_timeout,
                         prev->session_timeout, 300);

ngx_conf_merge_value(conf->prefer_server_ciphers,
                         prev->prefer_server_ciphers, 0);

ngx_conf_merge_bitmask_value(conf->protocols, prev->protocols,
                         (NGX_CONF_BITMASK_SET|NGX_SSL_DEFAULT_PROTOCOLS));

ngx_conf_merge_uint_value(conf->verify, prev->verify, 0);
    ngx_conf_merge_uint_value(conf->verify_depth, prev->verify_depth, 1);

ngx_conf_merge_ptr_value(conf->certificates, prev->certificates, NULL);
    ngx_conf_merge_ptr_value(conf->certificate_keys, prev->certificate_keys,
                         NULL);

ngx_conf_merge_ptr_value(conf->passwords, prev->passwords, NULL);

ngx_conf_merge_str_value(conf->dhparam, prev->dhparam, "");

ngx_conf_merge_str_value(conf->ecdh_curve, prev->ecdh_curve,
                         NGX_DEFAULT_ECDH_CURVE);

ngx_conf_merge_str_value(conf->client_certificate,
                         prev->client_certificate, "");
    ngx_conf_merge_str_value(conf->trusted_certificate,
                         prev->trusted_certificate, "");
    ngx_conf_merge_str_value(conf->crl, prev->crl, "");

ngx_conf_merge_str_value(conf->ciphers, prev->ciphers, NGX_DEFAULT_CIPHERS);

ngx_conf_merge_ptr_value(conf->conf_commands, prev->conf_commands, NULL);

conf->ssl.log = cf->log;

if (conf->listen) {
        mode = "listen ... ssl";

} else if (conf->starttls != NGX_MAIL_STARTTLS_OFF) {
        mode = "starttls";

} else {
        return NGX_CONF_OK;
    }

if (conf->file == NULL) {
        conf->file = prev->file;
        conf->line = prev->line;
    }

if (conf->certificates == NULL) {
        ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
                      "no \"ssl_certificate\" is defined for "
                      "the \"%s\" directive in %s:%ui",
                      mode, conf->file, conf->line);
        return NGX_CONF_ERROR;
    }

if (conf->certificate_keys == NULL) {
        ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
                      "no \"ssl_certificate_key\" is defined for "
                      "the \"%s\" directive in %s:%ui",
                      mode, conf->file, conf->line);
        return NGX_CONF_ERROR;
    }

if (conf->certificate_keys->nelts < conf->certificates->nelts) {
        ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
                      "no \"ssl_certificate_key\" is defined "
                      "for certificate \"%V\" and "
                      "the \"%s\" directive in %s:%ui",
                      ((ngx_str_t *) conf->certificates->elts)
                      + conf->certificates->nelts - 1,
                      mode, conf->file, conf->line);
        return NGX_CONF_ERROR;
    }

if (ngx_ssl_create(&conf->ssl, conf->protocols, NULL) != NGX_OK) {
        return NGX_CONF_ERROR;
    }

cln = ngx_pool_cleanup_add(cf->pool, 0);
    if (cln == NULL) {
        ngx_ssl_cleanup_ctx(&conf->ssl);
        return NGX_CONF_ERROR;
    }

cln->handler = ngx_ssl_cleanup_ctx;
    cln->data = &conf->ssl;

#ifdef TLSEXT_TYPE_application_layer_protocol_negotiation
    SSL_CTX_set_alpn_select_cb(conf->ssl.ctx, ngx_mail_ssl_alpn_select, NULL);
#endif

if (ngx_ssl_ciphers(cf, &conf->ssl, &conf->ciphers,
                        conf->prefer_server_ciphers)
        != NGX_OK)
    {
        return NGX_CONF_ERROR;
    }

if (ngx_ssl_certificates(cf, &conf->ssl, conf->certificates,
                             conf->certificate_keys, conf->passwords)
        != NGX_OK)
    {
        return NGX_CONF_ERROR;
    }

if (conf->verify) {

if (conf->verify != 3
            && conf->client_certificate.len == 0
            && conf->trusted_certificate.len == 0)
        {
            ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
                          "no ssl_client_certificate or "
                          "ssl_trusted_certificate for ssl_verify_client");
            return NGX_CONF_ERROR;
        }

if (ngx_ssl_client_certificate(cf, &conf->ssl,
                                       &conf->client_certificate,
                                       conf->verify_depth)
            != NGX_OK)
        {
            return NGX_CONF_ERROR;
        }

if (ngx_ssl_trusted_certificate(cf, &conf->ssl,
                                        &conf->trusted_certificate,
                                        conf->verify_depth)
            != NGX_OK)
        {
            return NGX_CONF_ERROR;
        }

if (ngx_ssl_crl(cf, &conf->ssl, &conf->crl) != NGX_OK) {
            return NGX_CONF_ERROR;
        }
    }

if (ngx_ssl_dhparam(cf, &conf->ssl, &conf->dhparam) != NGX_OK) {
        return NGX_CONF_ERROR;
    }

if (ngx_ssl_ecdh_curve(cf, &conf->ssl, &conf->ecdh_curve) != NGX_OK) {
        return NGX_CONF_ERROR;
    }

ngx_conf_merge_value(conf->builtin_session_cache,
                         prev->builtin_session_cache, NGX_SSL_NONE_SCACHE);

if (conf->shm_zone == NULL) {
        conf->shm_zone = prev->shm_zone;
    }

if (ngx_ssl_session_cache(&conf->ssl, &ngx_mail_ssl_sess_id_ctx,
                              conf->certificates, conf->builtin_session_cache,
                              conf->shm_zone, conf->session_timeout)
        != NGX_OK)
    {
        return NGX_CONF_ERROR;
    }

ngx_conf_merge_value(conf->session_tickets,
                         prev->session_tickets, 1);

#ifdef SSL_OP_NO_TICKET
    if (!conf->session_tickets) {
        SSL_CTX_set_options(conf->ssl.ctx, SSL_OP_NO_TICKET);
    }
#endif

ngx_conf_merge_ptr_value(conf->session_ticket_keys,
                         prev->session_ticket_keys, NULL);

if (ngx_ssl_session_ticket_keys(cf, &conf->ssl, conf->session_ticket_keys)
        != NGX_OK)
    {
        return NGX_CONF_ERROR;
    }

if (ngx_ssl_conf_commands(cf, &conf->ssl, conf->conf_commands) != NGX_OK) {
        return NGX_CONF_ERROR;
    }

return NGX_CONF_OK;
}

static char *
ngx_mail_ssl_starttls(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
    ngx_mail_ssl_conf_t  *scf = conf;

char  *rv;

rv = ngx_conf_set_enum_slot(cf, cmd, conf);

if (rv != NGX_CONF_OK) {
        return rv;
    }

if (!scf->listen) {
        scf->file = cf->conf_file->file.name.data;
        scf->line = cf->conf_file->line;
    }

return NGX_CONF_OK;
}

static char *
ngx_mail_ssl_password_file(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
    ngx_mail_ssl_conf_t  *scf = conf;

ngx_str_t  *value;

if (scf->passwords != NGX_CONF_UNSET_PTR) {
        return "is duplicate";
    }

value = cf->args->elts;

scf->passwords = ngx_ssl_read_password_file(cf, &value[1]);

if (scf->passwords == NULL) {
        return NGX_CONF_ERROR;
    }

return NGX_CONF_OK;
}

static char *
ngx_mail_ssl_session_cache(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
    ngx_mail_ssl_conf_t  *scf = conf;

size_t       len;
    ngx_str_t   *value, name, size;
    ngx_int_t    n;
    ngx_uint_t   i, j;

value = cf->args->elts;

for (i = 1; i < cf->args->nelts; i++) {

if (ngx_strcmp(value[i].data, "off") == 0) {
            scf->builtin_session_cache = NGX_SSL_NO_SCACHE;
            continue;
        }

if (ngx_strcmp(value[i].data, "none") == 0) {
            scf->builtin_session_cache = NGX_SSL_NONE_SCACHE;
            continue;
        }

if (ngx_strcmp(value[i].data, "builtin") == 0) {
            scf->builtin_session_cache = NGX_SSL_DFLT_BUILTIN_SCACHE;
            continue;
        }

if (value[i].len > sizeof("builtin:") - 1
            && ngx_strncmp(value[i].data, "builtin:", sizeof("builtin:") - 1)
               == 0)
        {
            n = ngx_atoi(value[i].data + sizeof("builtin:") - 1,
                         value[i].len - (sizeof("builtin:") - 1));

if (n == NGX_ERROR) {
                goto invalid;
            }

scf->builtin_session_cache = n;

continue;
        }

if (value[i].len > sizeof("shared:") - 1
            && ngx_strncmp(value[i].data, "shared:", sizeof("shared:") - 1)
               == 0)
        {
            len = 0;

for (j = sizeof("shared:") - 1; j < value[i].len; j++) {
                if (value[i].data[j] == ':') {
                    break;
                }

len++;
            }

if (len == 0 || j == value[i].len) {
                goto invalid;
            }

name.len = len;
            name.data = value[i].data + sizeof("shared:") - 1;

size.len = value[i].len - j - 1;
            size.data = name.data + len + 1;

n = ngx_parse_size(&size);

if (n == NGX_ERROR) {
                goto invalid;
            }

if (n < (ngx_int_t) (8 * ngx_pagesize)) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                   "session cache \"%V\" is too small",
                                   &value[i]);

return NGX_CONF_ERROR;
            }

scf->shm_zone = ngx_shared_memory_add(cf, &name, n,
                                                   &ngx_mail_ssl_module);
            if (scf->shm_zone == NULL) {
                return NGX_CONF_ERROR;
            }

scf->shm_zone->init = ngx_ssl_session_cache_init;

continue;
        }

goto invalid;
    }

if (scf->shm_zone && scf->builtin_session_cache == NGX_CONF_UNSET) {
        scf->builtin_session_cache = NGX_SSL_NO_BUILTIN_SCACHE;
    }

return NGX_CONF_OK;

invalid:

ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                       "invalid session cache \"%V\"", &value[i]);

return NGX_CONF_ERROR;
}

static char *
ngx_mail_ssl_conf_command_check(ngx_conf_t *cf, void *post, void *data)
{
#ifndef SSL_CONF_FLAG_FILE
    return "is not supported on this platform";
#else
    return NGX_CONF_OK;
#endif
}