/*
 * -----------------------------------------------------------------------------
 *
 * Author: Markus Moeller (markus_moeller at compuserve.com)
 *
 * Copyright (C) 2007 Markus Moeller. All rights reserved.
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; either version 2 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program; if not, write to the Free Software
 *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307, USA.
 *
 * -----------------------------------------------------------------------------
 */
/*
 * Hosted at http://sourceforge.net/projects/squidkerbauth
 */

#include <squid.h>

#if HAVE_KRB5 && HAVE_GSSAPI
#ifdef __cplusplus
extern "C" {
#endif

#if HAVE_PROFILE_H
#include <profile.h>
#endif				/* HAVE_PROFILE_H */
#if HAVE_KRB5_H
#if HAVE_BROKEN_SOLARIS_KRB5_H
#if defined(__cplusplus)
#define KRB5INT_BEGIN_DECLS     extern "C" {
#define KRB5INT_END_DECLS
    KRB5INT_BEGIN_DECLS
#endif
#endif
#include <krb5.h>
#elif HAVE_ET_COM_ERR_H
#include <et/com_err.h>
#endif                          /* HAVE_COM_ERR_H */
#if HAVE_COM_ERR_H
#include <com_err.h>
#endif				/* HAVE_COM_ERR_H */

#if HAVE_GSSAPI_GSSAPI_H
#include <gssapi/gssapi.h>
#elif HAVE_GSSAPI_H
#include <gssapi.h>
#endif				/* HAVE_GSSAPI_H */
#if HAVE_GSSAPI_GSSAPI_EXT_H
#include <gssapi/gssapi_ext.h>
#endif				/* HAVE_GSSAPI_GSSAPI_EXT_H */
#if HAVE_GSSAPI_GSSAPI_KRB5_H
#include <gssapi/gssapi_krb5.h>
#endif				/* HAVE_GSSAPI_GSSAPI_KRB5_H */
#if HAVE_GSSAPI_GSSAPI_GENERIC_H
#include <gssapi/gssapi_generic.h>
#endif				/* HAVE_GSSAPI_GSSAPI_GENERIC_H */

#ifndef gss_nt_service_name
#define gss_nt_service_name GSS_C_NT_HOSTBASED_SERVICE
#endif

#if !HAVE_ERROR_MESSAGE && HAVE_KRB5_GET_ERR_TEXT
#define error_message(code) krb5_get_err_text(kparam.context,code)
#elif  !HAVE_ERROR_MESSAGE && HAVE_KRB5_GET_ERROR_MESSAGE
#define error_message(code) krb5_get_error_message(kparam.context,code)
#elif !HAVE_ERROR_MESSAGE
    static char err_code[17];
    const char *KRB5_CALLCONV
    error_message(long code) {
        snprintf(err_code,16,"%ld",code);
        return err_code;
    }
#endif

#ifndef gss_mech_spnego
    static gss_OID_desc _gss_mech_spnego =
        { 6, (void *) "\x2b\x06\x01\x05\x05\x02" };
    gss_OID gss_mech_spnego = &_gss_mech_spnego;
#endif

#if HAVE_NAS_KERBEROS
#include <ibm_svc/krb5_svc.h>
    const char *KRB5_CALLCONV error_message(long code) {
        char *msg = NULL;
        krb5_svc_get_msg(code, &msg);
        return msg;
    }
#endif

    /*
     * Kerberos context and cache structure
     * Caches authentication details to reduce
     * number of authentication requests to kdc
     */
    static struct kstruct {
        krb5_context context;
        krb5_ccache cc;
    } kparam = {
        NULL, NULL};

    /*
     * krb5_create_cache creates a Kerberos file credential cache or a memory
     * credential cache if supported. The initial key for the principal
     * principal_name is extracted from the keytab keytab_filename.
     *
     * If keytab_filename is NULL the default will be used.
     * If principal_name is NULL the first working entry of the keytab will be used.
     */
    int krb5_create_cache(char *keytab_filename, char *principal_name);

    /*
     * krb5_cleanup clears used Keberos memory
     */
    void krb5_cleanup(void);

    /*
     * check_gss_err checks for gssapi error codes, extracts the error message
     * and prints it.
     */
    int check_gss_err(OM_uint32 major_status, OM_uint32 minor_status,
                      const char *function);

    int check_gss_err(OM_uint32 major_status, OM_uint32 minor_status,
                      const char *function) {
        if (GSS_ERROR(major_status)) {
            OM_uint32 maj_stat, min_stat;
            OM_uint32 msg_ctx = 0;
            gss_buffer_desc status_string;
            char buf[1024];
            size_t len;

            len = 0;
            msg_ctx = 0;
            while (!msg_ctx) {
                /* convert major status code (GSS-API error) to text */
                maj_stat = gss_display_status(&min_stat, major_status,
                                              GSS_C_GSS_CODE, GSS_C_NULL_OID, &msg_ctx, &status_string);
                if (maj_stat == GSS_S_COMPLETE) {
                    if (sizeof(buf) > len + status_string.length + 1) {
                        memcpy(buf + len, status_string.value,
                               status_string.length);
                        len += status_string.length;
                    }
                    gss_release_buffer(&min_stat, &status_string);
                    break;
                }
                gss_release_buffer(&min_stat, &status_string);
            }
            if (sizeof(buf) > len + 2) {
                strcpy(buf + len, ". ");
                len += 2;
            }
            msg_ctx = 0;
            while (!msg_ctx) {
                /* convert minor status code (underlying routine error) to text */
                maj_stat = gss_display_status(&min_stat, minor_status,
                                              GSS_C_MECH_CODE, GSS_C_NULL_OID, &msg_ctx, &status_string);
                if (maj_stat == GSS_S_COMPLETE) {
                    if (sizeof(buf) > len + status_string.length) {
                        memcpy(buf + len, status_string.value,
                               status_string.length);
                        len += status_string.length;
                    }
                    gss_release_buffer(&min_stat, &status_string);
                    break;
                }
                gss_release_buffer(&min_stat, &status_string);
            }
            debugs(11, 5, HERE << function << "failed: " << buf);
            return (1);
        }
        return (0);
    }

    void krb5_cleanup() {
        debugs(11, 5, HERE << "Cleanup kerberos context");
        if (kparam.context) {
            if (kparam.cc)
                krb5_cc_destroy(kparam.context, kparam.cc);
            kparam.cc = NULL;
            krb5_free_context(kparam.context);
            kparam.context = NULL;
        }
    }

    int krb5_create_cache(char *kf, char *pn) {

#define KT_PATH_MAX 256
#define MAX_RENEW_TIME "365d"
#define DEFAULT_SKEW (krb5_deltat) 600

        static char *keytab_filename = NULL, *principal_name = NULL;
        static krb5_keytab keytab = 0;
        static krb5_keytab_entry entry;
        static krb5_kt_cursor cursor;
        static krb5_creds *creds = NULL;
#if HAVE_HEIMDAL_KERBEROS
        static krb5_creds creds2;
#endif
        static krb5_principal principal = NULL;
        static krb5_deltat skew;

        krb5_get_init_creds_opt options;
        krb5_error_code code = 0;
        krb5_deltat rlife;
#if HAVE_PROFILE_H && HAVE_KRB5_GET_PROFILE && HAVE_PROFILE_GET_INTEGER && HAVE_PROFILE_RELEASE
        profile_t profile;
#endif
#if HAVE_HEIMDAL_KERBEROS
        krb5_kdc_flags flags;
        krb5_realm *client_realm;
#endif
        char *mem_cache;

restart:
        /*
         * Check if credentials need to be renewed
         */
        if (creds &&
                (creds->times.endtime - time(0) > skew) &&
                (creds->times.renew_till - time(0) > 2 * skew)) {
            if (creds->times.endtime - time(0) < 2 * skew) {
#if !HAVE_HEIMDAL_KERBEROS
                /* renew ticket */
                code =
                    krb5_get_renewed_creds(kparam.context, creds, principal,
                                           kparam.cc, NULL);
#else
                /* renew ticket */
                flags.i = 0;
                flags.b.renewable = flags.b.renew = 1;

                code =
                    krb5_cc_get_principal(kparam.context, kparam.cc,
                                          &creds2.client);
                if (code) {
                    debugs(11, 5,
                           HERE <<
                           "Error while getting principal from credential cache : "
                           << error_message(code));
                    return (1);
                }
                client_realm = krb5_princ_realm(kparam.context, creds2.client);
                code =
                    krb5_make_principal(kparam.context, &creds2.server,
                                        *client_realm, KRB5_TGS_NAME, *client_realm, NULL);
                if (code) {
                    debugs(11, 5,
                           HERE << "Error while getting krbtgt principal : " <<
                           error_message(code));
                    return (1);
                }
                code =
                    krb5_get_kdc_cred(kparam.context, kparam.cc, flags, NULL,
                                      NULL, &creds2, &creds);
                krb5_free_creds(kparam.context, &creds2);
#endif
                if (code) {
                    if (code == KRB5KRB_AP_ERR_TKT_EXPIRED) {
                        krb5_free_creds(kparam.context, creds);
                        creds = NULL;
                        /* this can happen because of clock skew */
                        goto restart;
                    }
                    debugs(11, 5,
                           HERE << "Error while get credentials : " <<
                           error_message(code));
                    return (1);
                }
            }
        } else {
            /* reinit */
            if (!kparam.context) {
                code = krb5_init_context(&kparam.context);
                if (code) {
                    debugs(11, 5,
                           HERE << "Error while initialising Kerberos library : "
                           << error_message(code));
                    return (1);
                }
            }
#if HAVE_PROFILE_H && HAVE_KRB5_GET_PROFILE && HAVE_PROFILE_GET_INTEGER && HAVE_PROFILE_RELEASE
            code = krb5_get_profile(kparam.context, &profile);
            if (code) {
                if (profile)
                    profile_release(profile);
                debugs(11, 5,
                       HERE << "Error while getting profile : " <<
                       error_message(code));
                return (1);
            }
            code =
                profile_get_integer(profile, "libdefaults", "clockskew", 0,
                                    5 * 60, &skew);
            if (profile)
                profile_release(profile);
            if (code) {
                debugs(11, 5,
                       HERE << "Error while getting clockskew : " <<
                       error_message(code));
                return (1);
            }
#elif HAVE_KRB5_GET_MAX_TIME_SKEW && HAVE_HEIMDAL_KERBEROS
            skew = krb5_get_max_time_skew(kparam.context);
#elif HAVE_MAX_SKEW_IN_KRB5_CONTEXT && HAVE_HEIMDAL_KERBEROS
            skew = kparam.context->max_skew;
#else
            skew = DEFAULT_SKEW;
#endif

            if (!kf) {
                char buf[KT_PATH_MAX], *p;

                krb5_kt_default_name(kparam.context, buf, KT_PATH_MAX);
                p = strchr(buf, ':');
                if (p)
                    p++;
                if (keytab_filename)
                    xfree(keytab_filename);
                keytab_filename = xstrdup(p ? p : buf);
            } else {
                keytab_filename = xstrdup(kf);
            }

            code = krb5_kt_resolve(kparam.context, keytab_filename, &keytab);
            if (code) {
                debugs(11, 5,
                       HERE << "Error while resolving keytab filename " <<
                       keytab_filename << " : " << error_message(code));
                return (1);
            }

            if (!pn) {
                code = krb5_kt_start_seq_get(kparam.context, keytab, &cursor);
                if (code) {
                    debugs(11, 5,
                           HERE << "Error while starting keytab scan : " <<
                           error_message(code));
                    return (1);
                }
                code =
                    krb5_kt_next_entry(kparam.context, keytab, &entry, &cursor);
                krb5_copy_principal(kparam.context, entry.principal,
                                    &principal);
                if (code && code != KRB5_KT_END) {
                    debugs(11, 5,
                           HERE << "Error while scanning keytab : " <<
                           error_message(code));
                    return (1);
                }

                code = krb5_kt_end_seq_get(kparam.context, keytab, &cursor);
                if (code) {
                    debugs(11, 5,
                           HERE << "Error while ending keytab scan : " <<
                           error_message(code));
                    return (1);
                }
#if HAVE_HEIMDAL_KERBEROS || ( HAVE_KRB5_KT_FREE_ENTRY && HAVE_DECL_KRB5_KT_FREE_ENTRY)
                code = krb5_kt_free_entry(kparam.context, &entry);
#else
                code = krb5_free_keytab_entry_contents(kparam.context, &entry);
#endif
                if (code) {
                    debugs(11, 5,
                           HERE << "Error while freeing keytab entry : " <<
                           error_message(code));
                    return (1);
                }

            } else {
                principal_name = xstrdup(pn);
            }

            if (!principal) {
                code =
                    krb5_parse_name(kparam.context, principal_name, &principal);
                if (code) {
                    debugs(11, 5,
                           HERE << "Error while parsing principal name " <<
                           principal_name << " : " << error_message(code));
                    return (1);
                }
            }

            creds = (krb5_creds *) xmalloc(sizeof(*creds));
            memset(creds, 0, sizeof(*creds));
            krb5_get_init_creds_opt_init(&options);
            code = krb5_string_to_deltat((char *) MAX_RENEW_TIME, &rlife);
            if (code != 0 || rlife == 0) {
                debugs(11, 5,
                       HERE << "Error bad lifetime value " << MAX_RENEW_TIME <<
                       " : " << error_message(code));
                return (1);
            }
            krb5_get_init_creds_opt_set_renew_life(&options, rlife);

            code =
                krb5_get_init_creds_keytab(kparam.context, creds, principal,
                                           keytab, 0, NULL, &options);
            if (code) {
                debugs(11, 5,
                       HERE <<
                       "Error while initializing credentials from keytab : " <<
                       error_message(code));
                return (1);
            }
#if !HAVE_KRB5_MEMORY_CACHE
            mem_cache =
                (char *) xmalloc(strlen("FILE:/tmp/peer_proxy_negotiate_auth_")
                                 + 16);
            snprintf(mem_cache,
                     strlen("FILE:/tmp/peer_proxy_negotiate_auth_") + 16,
                     "FILE:/tmp/peer_proxy_negotiate_auth_%d", (int) getpid());
#else
            mem_cache =
                (char *) xmalloc(strlen("MEMORY:peer_proxy_negotiate_auth_") +
                                 16);
            snprintf(mem_cache,
                     strlen("MEMORY:peer_proxy_negotiate_auth_") + 16,
                     "MEMORY:peer_proxy_negotiate_auth_%d", (int) getpid());
#endif

            setenv("KRB5CCNAME", mem_cache, 1);
            code = krb5_cc_resolve(kparam.context, mem_cache, &kparam.cc);
            if (mem_cache)
                xfree(mem_cache);
            if (code) {
                debugs(11, 5,
                       HERE << "Error while resolving memory credential cache : "
                       << error_message(code));
                return (1);
            }
            code = krb5_cc_initialize(kparam.context, kparam.cc, principal);
            if (code) {
                debugs(11, 5,
                       HERE <<
                       "Error while initializing memory credential cache : " <<
                       error_message(code));
                return (1);
            }
            code = krb5_cc_store_cred(kparam.context, kparam.cc, creds);
            if (code) {
                debugs(11, 5,
                       HERE << "Error while storing credentials : " <<
                       error_message(code));
                return (1);
            }

            if (!creds->times.starttime)
                creds->times.starttime = creds->times.authtime;
        }
        return (0);
    }

    /*
     * peer_proxy_negotiate_auth gets a GSSAPI token for principal_name
     * and base64 encodes it.
     */
    char *peer_proxy_negotiate_auth(char *principal_name, char *proxy) {
        int rc = 0;
        OM_uint32 major_status, minor_status;
        gss_ctx_id_t gss_context = GSS_C_NO_CONTEXT;
        gss_name_t server_name = GSS_C_NO_NAME;
        gss_buffer_desc service = GSS_C_EMPTY_BUFFER;
        gss_buffer_desc input_token = GSS_C_EMPTY_BUFFER;
        gss_buffer_desc output_token = GSS_C_EMPTY_BUFFER;
        char *token = NULL;

        setbuf(stdout, NULL);
        setbuf(stdin, NULL);

        if (!proxy) {
            debugs(11, 5, HERE << "Error : No proxy server name");
            return NULL;
        }

        if (principal_name)
            debugs(11, 5,
                   HERE << "Creating credential cache for " << principal_name);
        else
            debugs(11, 5, HERE << "Creating credential cache");
        rc = krb5_create_cache(NULL, principal_name);
        if (rc) {
            debugs(11, 5, HERE << "Error : Failed to create Kerberos cache");
            krb5_cleanup();
            return NULL;
        }

        service.value = (void *) xmalloc(strlen("HTTP") + strlen(proxy) + 2);
        snprintf((char *) service.value, strlen("HTTP") + strlen(proxy) + 2,
                 "%s@%s", "HTTP", proxy);
        service.length = strlen((char *) service.value);

        debugs(11, 5, HERE << "Import gss name");
        major_status = gss_import_name(&minor_status, &service,
                                       gss_nt_service_name, &server_name);

        if (check_gss_err(major_status, minor_status, "gss_import_name()"))
            goto cleanup;

        debugs(11, 5, HERE << "Initialize gss security context");
        major_status = gss_init_sec_context(&minor_status,
                                            GSS_C_NO_CREDENTIAL,
                                            &gss_context,
                                            server_name,
                                            gss_mech_spnego,
                                            0,
                                            0,
                                            GSS_C_NO_CHANNEL_BINDINGS,
                                            &input_token, NULL, &output_token, NULL, NULL);

        if (check_gss_err(major_status, minor_status, "gss_init_sec_context()"))
            goto cleanup;

        debugs(11, 5, HERE << "Got token with length " << output_token.length);
        if (output_token.length) {

            token =
                (char *) base64_encode_bin((const char *) output_token.value,
                                           output_token.length);
        }


cleanup:
        gss_delete_sec_context(&minor_status, &gss_context, NULL);
        gss_release_buffer(&minor_status, &service);
        gss_release_buffer(&minor_status, &input_token);
        gss_release_buffer(&minor_status, &output_token);
        gss_release_name(&minor_status, &server_name);

        return token;
    }

#ifdef __cplusplus
}
#endif
#endif /* HAVE_KRB5 && HAVE_GSSAPI */
