Add a credential cache back end structure

To be able to add support for new credential cache types easily, this
patch creates a new structure sss_krb5_cc_be that defines common
operations with a credential cache, such as create, check if used or remove.

7 files changed, 382 insertions, 148 deletions

diff --git a/src/providers/krb5/krb5_auth.c b/src/providers/krb5/krb5_auth.c
index 7c622dbe..9b503f47 100644
--- a/src/providers/krb5/krb5_auth.c
+++ b/src/providers/krb5/krb5_auth.c
@@ -39,107 +39,76 @@
 #include "providers/krb5/krb5_auth.h"
 #include "providers/krb5/krb5_utils.h"
 
-static errno_t safe_remove_old_ccache_file(const char *old_ccache_file,
-                                           const char *new_ccache_file)
+static errno_t safe_remove_old_ccache_file(struct sss_krb5_cc_be *cc_be,
+                                           const char *princ,
+                                           const char *old_ccache,
+                                           const char *new_ccache)
 {
     int ret;
-    size_t old_offset = 0;
-    size_t new_offset = 0;
+    enum sss_krb5_cc_type old_type;
+    struct sss_krb5_cc_be *old_cc_ops;
 
-    if (new_ccache_file == NULL) {
-        DEBUG(1, ("Missing new ccache file, "
-                  "old ccache file is not deleted.\n"));
-        return EINVAL;
+    if (old_ccache == NULL) {
+        DEBUG(SSSDBG_FUNC_DATA, ("No old ccache, nothing to do\n"));
+        return EOK;
     }
 
-    if (old_ccache_file != NULL) {
-        if (strncmp(old_ccache_file, "FILE:", 5) == 0) {
-            old_offset = 5;
-        }
-        if (strncmp(new_ccache_file, "FILE:", 5) == 0) {
-            new_offset = 5;
-        }
-        if (strcmp(old_ccache_file + old_offset,
-                   new_ccache_file + new_offset) == 0) {
-            DEBUG(7, ("New and old ccache file are the same, "
-                      "no one will be deleted.\n"));
-            return EOK;
-        }
-        if (old_ccache_file[old_offset] != '/') {
-            DEBUG(1, ("Ccache file name [%s] is not an absolute path.\n",
-                      old_ccache_file + old_offset));
-            return EINVAL;
-        }
-        ret = unlink(old_ccache_file + old_offset);
-        if (ret == -1 && errno != ENOENT) {
-            ret = errno;
-            DEBUG(1, ("unlink [%s] failed [%d][%s].\n", old_ccache_file, ret,
-                                                        strerror(ret)));
-            return ret;
-        }
+    if (new_ccache == NULL) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              ("Missing new ccache file, old ccache file is not deleted.\n"));
+        return EINVAL;
     }
 
-    return EOK;
-}
-
-static errno_t check_if_ccache_file_is_used(uid_t uid, const char *ccname,
-                                            bool *result)
-{
-    int ret;
-    size_t offset = 0;
-    struct stat stat_buf;
-    const char *filename;
-    bool active;
-
-    *result = false;
-
-    if (ccname == NULL || *ccname == '\0') {
+    old_type = sss_krb5_get_type(old_ccache);
+    old_cc_ops = get_cc_be_ops(old_type);
+    if (!old_cc_ops) {
+        DEBUG(SSSDBG_CRIT_FAILURE, ("Cannot get ccache operations\n"));
         return EINVAL;
     }
 
-    if (strncmp(ccname, "FILE:", 5) == 0) {
-        offset = 5;
+    if (cc_be->type == old_type &&
+        strcmp(old_ccache, new_ccache) == 0) {
+        DEBUG(SSSDBG_TRACE_FUNC, ("New and old ccache file are the same, "
+                                  "no one will be deleted.\n"));
+        return EOK;
     }
 
-    filename = ccname + offset;
-
-    if (filename[0] != '/') {
-        DEBUG(1, ("Only absolute path names are allowed.\n"));
-        return EINVAL;
+    ret = old_cc_ops->remove(old_ccache);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_CRIT_FAILURE,
+                ("Cannot remove ccache [%s]\n", old_ccache));
+        return EIO;
     }
 
-    ret = lstat(filename, &stat_buf);
+    return EOK;
+}
 
-    if (ret == -1 && errno != ENOENT) {
-        DEBUG(1, ("stat failed [%d][%s].\n", errno, strerror(errno)));
-        return errno;
-    } else if (ret == EOK) {
-        if (stat_buf.st_uid != uid) {
-            DEBUG(1, ("Cache file [%s] exists, but is owned by [%d] instead of "
-                      "[%d].\n", filename, stat_buf.st_uid, uid));
-            return EINVAL;
-        }
+static errno_t
+check_old_ccache(const char *old_ccache, struct krb5child_req *kr,
+                 const char *realm, bool *active, bool *valid)
+{
+    struct sss_krb5_cc_be *old_cc_ops;
+    errno_t ret;
 
-        if (!S_ISREG(stat_buf.st_mode)) {
-            DEBUG(1, ("Cache file [%s] exists, but is not a regular file.\n",
-                      filename));
-            return EINVAL;
-        }
+    /* ccache file might be of a different type if the user changed
+     * configuration
+     */
+    old_cc_ops = get_cc_be_ops_ccache(old_ccache);
+    if (old_cc_ops == NULL) {
+        DEBUG(SSSDBG_CRIT_FAILURE,
+              ("Cannot get operations on saved ccache %s\n", old_ccache));
+        return EINVAL;
     }
 
-    ret = check_if_uid_is_active(uid, &active);
+    ret = old_cc_ops->check_existing(old_ccache, kr->uid, realm,
+                                     kr->upn, active, valid);
     if (ret != EOK) {
-        DEBUG(1, ("check_if_uid_is_active failed.\n"));
+        DEBUG(SSSDBG_OP_FAILURE,
+              ("Cannot check if saved ccache %s is active and valid\n",
+               old_ccache));
         return ret;
     }
 
-    if (!active) {
-        DEBUG(5, ("User [%d] is not active\n", uid));
-    } else {
-        DEBUG(9, ("User [%d] is still active, reusing ccache file [%s].\n",
-                  uid, filename));
-        *result = true;
-    }
     return EOK;
 }
 
@@ -332,7 +301,6 @@ struct tevent_req *krb5_auth_send(TALLOC_CTX *mem_ctx,
     struct krb5child_req *kr = NULL;
     const char *ccache_file = NULL;
     const char *realm;
-    krb5_error_code kerr;
     struct tevent_req *req;
     struct tevent_req *subreq;
     int ret;
@@ -457,22 +425,20 @@ struct tevent_req *krb5_auth_send(TALLOC_CTX *mem_ctx,
             goto done;
         }
 
+        /* The type of the ccache might change during the request if we
+         * end up reusing an old ccache */
+        kr->cc_be = krb5_ctx->cc_be;
+
         ccache_file = ldb_msg_find_attr_as_string(res->msgs[0],
                                                   SYSDB_CCACHE_FILE,
                                                   NULL);
         if (ccache_file != NULL) {
-            ret = check_if_ccache_file_is_used(kr->uid, ccache_file,
-                                               &kr->active_ccache_present);
+            ret = check_old_ccache(ccache_file, kr, realm,
+                                   &kr->active_ccache_present,
+                                   &kr->valid_tgt_present);
             if (ret != EOK) {
-                DEBUG(1, ("check_if_ccache_file_is_used failed.\n"));
-                goto done;
-            }
-
-            kerr = check_for_valid_tgt(ccache_file, realm, kr->upn,
-                                       &kr->valid_tgt_present);
-            if (kerr != 0) {
-                DEBUG(1, ("check_for_valid_tgt failed.\n"));
-                ret = kerr;
+                DEBUG(SSSDBG_CRIT_FAILURE,
+                      ("check_if_ccache_file_is_used failed.\n"));
                 goto done;
             }
         } else {
@@ -639,13 +605,27 @@ static void krb5_find_ccache_step(struct tevent_req *req)
                 goto done;
             }
 
-            ret = create_ccache_dir(kr, kr->ccname,
+            ret = kr->cc_be->create(kr->ccname,
                                     kr->krb5_ctx->illegal_path_re,
                                     kr->uid, kr->gid, private_path);
             if (ret != EOK) {
-                DEBUG(1, ("create_ccache_dir failed.\n"));
+                DEBUG(SSSDBG_OP_FAILURE, ("ccache creation failed.\n"));
                 goto done;
             }
+    } else {
+        DEBUG(SSSDBG_MINOR_FAILURE,
+              ("Saved ccache %s if of different type than ccache in "
+               "configuration file, reusing the old ccache\n"));
+
+        kr->cc_be = get_cc_be_ops_ccache(kr->old_ccname);
+        if (kr->cc_be == NULL) {
+            DEBUG(SSSDBG_CRIT_FAILURE,
+                  ("Cannot get operations on saved ccache %s\n",
+                   kr->old_ccname));
+            ret = EINVAL;
+            goto done;
+        }
+
     }
 
     if (kr->is_offline) {
@@ -725,6 +705,7 @@ static void krb5_child_done(struct tevent_req *subreq)
     uint8_t *buf = NULL;
     ssize_t len = -1;
     struct krb5_child_response *res;
+    const char *store_ccname;
 
     ret = handle_child_recv(subreq, pd, &buf, &len);
     talloc_zfree(subreq);
@@ -777,7 +758,8 @@ static void krb5_child_done(struct tevent_req *subreq)
     if (res->msg_status == PAM_NEW_AUTHTOK_REQD) {
         if (pd->cmd == SSS_PAM_AUTHENTICATE && !kr->active_ccache_present) {
             if (kr->old_ccname != NULL) {
-                ret = safe_remove_old_ccache_file(kr->old_ccname, "dummy");
+                ret = safe_remove_old_ccache_file(kr->cc_be, kr->upn,
+                                                  kr->old_ccname, "dummy");
                 if (ret != EOK) {
                     DEBUG(1, ("Failed to remove old ccache file [%s], "
                               "please remove it manually.\n", kr->old_ccname));
@@ -851,16 +833,25 @@ static void krb5_child_done(struct tevent_req *subreq)
         goto done;
     }
 
-    if (kr->old_ccname != NULL) {
-        ret = safe_remove_old_ccache_file(kr->old_ccname, kr->ccname);
-        if (ret != EOK) {
-            DEBUG(1, ("Failed to remove old ccache file [%s], "
-                      "please remove it manually.\n", kr->old_ccname));
-        }
+    store_ccname = kr->cc_be->ccache_for_princ(kr, kr->ccname,
+                                               kr->upn);
+    if (store_ccname == NULL) {
+        DEBUG(SSSDBG_CRIT_FAILURE,
+                ("No ccache for %s in %s?\n", kr->upn, kr->ccname));
+        ret = EIO;
+        goto done;
+    }
+
+    ret = safe_remove_old_ccache_file(kr->cc_be, kr->upn,
+                                      kr->old_ccname, store_ccname);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_MINOR_FAILURE,
+              ("Failed to remove old ccache file [%s], "
+               "please remove it manually.\n", kr->old_ccname));
     }
 
     ret = krb5_save_ccname(state, state->be_ctx->sysdb,
-                           pd->user, kr->ccname);
+                           pd->user, store_ccname);
     if (ret) {
         DEBUG(1, ("krb5_save_ccname failed.\n"));
         goto done;
diff --git a/src/providers/krb5/krb5_auth.h b/src/providers/krb5/krb5_auth.h
index 5cc22dfe..cc079ba9 100644
--- a/src/providers/krb5/krb5_auth.h
+++ b/src/providers/krb5/krb5_auth.h
@@ -41,6 +41,7 @@ struct krb5child_req {
     struct pam_data *pd;
     struct krb5_ctx *krb5_ctx;
 
+    struct sss_krb5_cc_be *cc_be;
     const char *ccname;
     const char *old_ccname;
     const char *homedir;
diff --git a/src/providers/krb5/krb5_become_user.c b/src/providers/krb5/krb5_become_user.c
index 351f539a..cc4e6a58 100644
--- a/src/providers/krb5/krb5_become_user.c
+++ b/src/providers/krb5/krb5_become_user.c
@@ -31,7 +31,7 @@ errno_t become_user(uid_t uid, gid_t gid)
 {
     int ret;
 
-    DEBUG(9, ("Trying to become user [%d][%d].\n", uid, gid));
+    DEBUG(SSSDBG_FUNC_DATA, ("Trying to become user [%d][%d].\n", uid, gid));
     ret = setgid(gid);
     if (ret == -1) {
         DEBUG(1, ("setgid failed [%d][%s].\n", errno, strerror(errno)));
diff --git a/src/providers/krb5/krb5_common.c b/src/providers/krb5/krb5_common.c
index 022745d6..91816662 100644
--- a/src/providers/krb5/krb5_common.c
+++ b/src/providers/krb5/krb5_common.c
@@ -31,6 +31,7 @@
 #include "providers/dp_backend.h"
 #include "providers/krb5/krb5_common.h"
 #include "providers/krb5/krb5_opts.h"
+#include "providers/krb5/krb5_utils.h"
 
 errno_t check_and_export_lifetime(struct dp_option *opts, const int opt_id,
                                   const char *env_name)
@@ -95,6 +96,7 @@ errno_t check_and_export_options(struct dp_option *opts,
     const char *dummy;
     char *use_fast_str;
     char *fast_principal;
+    enum sss_krb5_cc_type cc_be;
 
     realm = dp_opt_get_cstring(opts, KRB5_REALM);
     if (realm == NULL) {
@@ -178,11 +180,15 @@ errno_t check_and_export_options(struct dp_option *opts,
         DEBUG(1, ("Missing credential cache name template.\n"));
         return EINVAL;
     }
-    if (dummy[0] != '/' && strncmp(dummy, "FILE:", 5) != 0) {
-        DEBUG(1, ("Currently only file based credential caches are supported "
-                  "and krb5ccname_template must start with '/' or 'FILE:'\n"));
+
+    cc_be = sss_krb5_get_type(dummy);
+    if (cc_be != SSS_KRB5_TYPE_FILE || dummy[0] != '/') {
+        DEBUG(SSSDBG_CONF_SETTINGS,
+              ("Currently only file based credential caches are supported "
+               "and krb5ccname_template must start with '/' or 'FILE:'\n"));
         return EINVAL;
     }
+    krb5_ctx->cc_be = &file_cc;
 
     return EOK;
 }
diff --git a/src/providers/krb5/krb5_common.h b/src/providers/krb5/krb5_common.h
index 950505f1..029ebf6e 100644
--- a/src/providers/krb5/krb5_common.h
+++ b/src/providers/krb5/krb5_common.h
@@ -84,6 +84,7 @@ struct krb5_service {
 struct fo_service;
 struct deferred_auth_ctx;
 struct renew_tgt_ctx;
+struct sss_krb5_cc_be;
 
 struct krb5_ctx {
     /* opts taken from kinit */
@@ -115,6 +116,7 @@ struct krb5_ctx {
     struct krb5_service *kpasswd_service;
     int child_debug_fd;
 
+    struct sss_krb5_cc_be *cc_be;
     pcre *illegal_path_re;
 
     struct deferred_auth_ctx *deferred_auth_ctx;
@@ -171,4 +173,5 @@ errno_t remove_krb5_info_files(TALLOC_CTX *mem_ctx, const char *realm);
 
 errno_t krb5_get_simple_upn(TALLOC_CTX *mem_ctx, struct krb5_ctx *krb5_ctx,
                             const char *username, const char **_upn);
+
 #endif /* __KRB5_COMMON_H__ */
diff --git a/src/providers/krb5/krb5_utils.c b/src/providers/krb5/krb5_utils.c
index 9d199e1f..9f02fe33 100644
--- a/src/providers/krb5/krb5_utils.c
+++ b/src/providers/krb5/krb5_utils.c
@@ -26,6 +26,7 @@
 
 #include "providers/krb5/krb5_utils.h"
 #include "providers/krb5/krb5_auth.h"
+#include "src/util/find_uid.h"
 #include "util/util.h"
 
 char *expand_ccname_template(TALLOC_CTX *mem_ctx, struct krb5child_req *kr,
@@ -307,38 +308,46 @@ done:
     return ret;
 }
 
-errno_t create_ccache_dir(TALLOC_CTX *mem_ctx, const char *filename,
-                          pcre *illegal_re, uid_t uid, gid_t gid,
-                          bool private_path)
+static errno_t
+check_ccache_re(const char *filename, pcre *illegal_re)
+{
+    errno_t ret;
+
+    ret = pcre_exec(illegal_re, NULL, filename, strlen(filename),
+                    0, 0, NULL, 0);
+    if (ret == 0) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              ("Illegal pattern in ccache directory name [%s].\n", filename));
+        return EINVAL;
+    } else if (ret == PCRE_ERROR_NOMATCH) {
+        DEBUG(SSSDBG_TRACE_LIBS,
+              ("Ccache directory name [%s] does not contain "
+               "illegal patterns.\n", filename));
+        return EOK;
+    }
+
+    DEBUG(SSSDBG_CRIT_FAILURE, ("pcre_exec failed [%d].\n", ret));
+    return EFAULT;
+}
+
+static errno_t
+create_ccache_dir(const char *dirname, pcre *illegal_re,
+                  uid_t uid, gid_t gid, bool private_path)
 {
     int ret = EFAULT;
-    char *dirname;
-    char *end;
     struct stat parent_stat;
     struct string_list *missing_parents = NULL;
     struct string_list *li = NULL;
     mode_t old_umask;
     mode_t new_dir_mode;
-    size_t offset = 0;
     TALLOC_CTX *tmp_ctx = NULL;
 
-    tmp_ctx = talloc_new(mem_ctx);
+    tmp_ctx = talloc_new(NULL);
     if (tmp_ctx == NULL) {
         DEBUG(1, ("talloc_new failed.\n"));
         return ENOMEM;
     }
 
-    if (strncmp(filename, "FILE:", 5) == 0) {
-        offset = 5;
-    }
-
-    dirname = talloc_strdup(tmp_ctx, filename + offset);
-    if (dirname == NULL) {
-        DEBUG(1, ("talloc_strndup failed.\n"));
-        ret = ENOMEM;
-        goto done;
-    }
-
     if (*dirname != '/') {
         DEBUG(1, ("Only absolute paths are allowed, not [%s] .\n", dirname));
         ret = EINVAL;
@@ -346,31 +355,12 @@ errno_t create_ccache_dir(TALLOC_CTX *mem_ctx, const char *filename,
     }
 
     if (illegal_re != NULL) {
-        ret = pcre_exec(illegal_re, NULL, dirname, strlen(dirname),
-                        0, 0, NULL, 0);
-        if (ret == 0) {
-            DEBUG(1, ("Illegal pattern in ccache directory name [%s].\n",
-                      dirname));
-            ret = EINVAL;
-            goto done;
-        } else if ( ret == PCRE_ERROR_NOMATCH) {
-            DEBUG(9, ("Ccache directory name [%s] does not contain "
-                      "illegal patterns.\n", dirname));
-        } else {
-            DEBUG(1, ("pcre_exec failed [%d].\n", ret));
-            ret = EFAULT;
+        ret = check_ccache_re(dirname, illegal_re);
+        if (ret != EOK) {
             goto done;
         }
     }
 
-    end = strrchr(dirname, '/');
-    if (end == NULL || end == dirname) {
-        DEBUG(1, ("Missing filename in [%s].\n", dirname));
-        ret = EINVAL;
-        goto done;
-    }
-    *end = '\0';
-
     ret = find_ccdir_parent_data(tmp_ctx, dirname, &parent_stat,
                                  &missing_parents);
     if (ret != EOK) {
@@ -527,3 +517,221 @@ done:
 
     return EOK;
 }
+
+/*======== ccache back end utilities ========*/
+struct sss_krb5_cc_be *
+get_cc_be_ops(enum sss_krb5_cc_type type)
+{
+    struct sss_krb5_cc_be *be;
+
+    switch (type) {
+        case SSS_KRB5_TYPE_FILE:
+            be = &file_cc;
+            break;
+        case SSS_KRB5_TYPE_UNKNOWN:
+            be = NULL;
+            break;
+    }
+
+    return be;
+}
+
+struct sss_krb5_cc_be *
+get_cc_be_ops_ccache(const char *ccache)
+{
+    enum sss_krb5_cc_type type;
+
+    type = sss_krb5_get_type(ccache);
+    return get_cc_be_ops(type);
+}
+
+/*======== Operations on the FILE: back end ========*/
+errno_t
+cc_file_create(const char *location, pcre *illegal_re,
+               uid_t uid, gid_t gid, bool private_path)
+{
+    const char *filename;
+    char *dirname;
+    char *end;
+    TALLOC_CTX *tmp_ctx = NULL;
+    errno_t ret;
+
+    filename = sss_krb5_residual_check_type(location, SSS_KRB5_TYPE_FILE);
+    if (filename == NULL) {
+        DEBUG(SSSDBG_OP_FAILURE, ("Bad ccache type %s\n", location));
+        return EINVAL;
+    }
+
+    tmp_ctx = talloc_new(NULL);
+    if (tmp_ctx == NULL) {
+        DEBUG(SSSDBG_CRIT_FAILURE, ("talloc_new failed.\n"));
+        return ENOMEM;
+    }
+
+    dirname = talloc_strdup(tmp_ctx, filename);
+    if (dirname == NULL) {
+        DEBUG(SSSDBG_CRIT_FAILURE, ("talloc_strdup failed.\n"));
+        ret = ENOMEM;
+        goto done;
+    }
+
+    end = strrchr(dirname, '/');
+    if (end == NULL || end == dirname) {
+        DEBUG(SSSDBG_CRIT_FAILURE, ("Missing filename in [%s].\n", dirname));
+        ret = EINVAL;
+        goto done;
+    }
+    *end = '\0';
+
+    ret = create_ccache_dir(dirname, illegal_re, uid, gid, private_path);
+done:
+    talloc_free(tmp_ctx);
+    return ret;
+}
+
+static errno_t
+cc_residual_is_used(uid_t uid, const char *ccname,
+                    enum sss_krb5_cc_type type, bool *result)
+{
+    int ret;
+    struct stat stat_buf;
+    bool active;
+
+    *result = false;
+
+    if (ccname == NULL || *ccname == '\0') {
+        return EINVAL;
+    }
+
+    ret = lstat(ccname, &stat_buf);
+
+    if (ret == -1 && errno != ENOENT) {
+        ret = errno;
+        DEBUG(SSSDBG_OP_FAILURE,
+              ("stat failed [%d][%s].\n", ret, strerror(ret)));
+        return ret;
+    } else if (ret == EOK) {
+        if (stat_buf.st_uid != uid) {
+            DEBUG(SSSDBG_OP_FAILURE,
+                  ("Cache file [%s] exists, but is owned by [%d] instead of "
+                   "[%d].\n", ccname, stat_buf.st_uid, uid));
+            return EINVAL;
+        }
+
+        switch (type) {
+            case SSS_KRB5_TYPE_FILE:
+                ret = S_ISREG(stat_buf.st_mode);
+                break;
+            default:
+                DEBUG(SSSDBG_CRIT_FAILURE, ("Unsupported ccache type\n"));
+                return EINVAL;
+        }
+
+        if (ret == 0) {
+            DEBUG(SSSDBG_OP_FAILURE,
+                  ("Cache file [%s] exists, but is not the expected type\n",
+                   ccname));
+            return EINVAL;
+        }
+    }
+
+    ret = check_if_uid_is_active(uid, &active);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE, ("check_if_uid_is_active failed.\n"));
+        return ret;
+    }
+
+    if (!active) {
+        DEBUG(SSSDBG_TRACE_FUNC, ("User [%d] is not active\n", uid));
+    } else {
+        DEBUG(SSSDBG_TRACE_LIBS,
+              ("User [%d] is still active, reusing ccache [%s].\n",
+              uid, ccname));
+        *result = true;
+    }
+    return EOK;
+}
+
+errno_t
+cc_file_check_existing(const char *location, uid_t uid,
+                       const char *realm, const char *princ,
+                       bool *_active, bool *_valid)
+{
+    errno_t ret;
+    bool active;
+    bool valid;
+    const char *filename;
+
+    filename = sss_krb5_residual_check_type(location, SSS_KRB5_TYPE_FILE);
+    if (!filename) {
+        DEBUG(SSSDBG_CRIT_FAILURE, ("%s is not of type FILE:\n"));
+        return EINVAL;
+    }
+
+    if (filename[0] != '/') {
+        DEBUG(SSSDBG_OP_FAILURE, ("Only absolute path names are allowed.\n"));
+        return EINVAL;
+    }
+
+    ret = cc_residual_is_used(uid, filename, SSS_KRB5_TYPE_FILE, &active);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE, ("Could not check if ccache is active\n"));
+        return ret;
+    }
+
+    ret = check_for_valid_tgt(location, realm, princ, &valid);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              ("Could not check if ccache contains a valid principal\n"));
+        return ret;
+    }
+
+    *_active = active;
+    *_valid = valid;
+    return EOK;
+}
+
+const char *
+cc_file_cache_for_princ(TALLOC_CTX *mem_ctx, const char *location,
+                        const char *princ)
+{
+    return talloc_strdup(mem_ctx, location);
+}
+
+errno_t
+cc_file_remove(const char *location)
+{
+    errno_t ret;
+    const char *filename;
+
+    filename = sss_krb5_residual_check_type(location, SSS_KRB5_TYPE_FILE);
+    if (!filename) {
+        DEBUG(SSSDBG_CRIT_FAILURE, ("%s is not of type FILE:\n"));
+        return EINVAL;
+    }
+
+    if (filename[0] != '/') {
+        DEBUG(SSSDBG_CRIT_FAILURE,
+              ("Ccache file name [%s] is not an absolute path.\n", filename));
+        return EINVAL;
+    }
+
+    errno = 0;
+    ret = unlink(filename);
+    if (ret == -1 && errno != ENOENT) {
+        ret = errno;
+        DEBUG(SSSDBG_CRIT_FAILURE,
+              ("unlink [%s] failed [%d][%s].\n", filename, ret,
+                                                 strerror(ret)));
+        return ret;
+    }
+    return EOK;
+}
+
+struct sss_krb5_cc_be file_cc = {
+    .type               = SSS_KRB5_TYPE_FILE,
+    .create             = cc_file_create,
+    .check_existing     = cc_file_check_existing,
+    .ccache_for_princ   = cc_file_cache_for_princ,
+    .remove             = cc_file_remove,
+};
diff --git a/src/providers/krb5/krb5_utils.h b/src/providers/krb5/krb5_utils.h
index 7cc57d42..87bba2ba 100644
--- a/src/providers/krb5/krb5_utils.h
+++ b/src/providers/krb5/krb5_utils.h
@@ -31,16 +31,41 @@
 #include "providers/krb5/krb5_auth.h"
 #include "providers/data_provider.h"
 
+/* Operations on a credential cache */
+typedef errno_t (*cc_be_create_fn)(const char *location, pcre *illegal_re,
+                                   uid_t uid, gid_t gid, bool private_path);
+typedef errno_t (*cc_be_check_existing)(const char *location, uid_t uid,
+                                        const char *realm, const char *princ,
+                                        bool *active, bool *valid);
+typedef const char * (*cc_be_ccache_for_princ)(TALLOC_CTX *mem_ctx,
+                                               const char *location,
+                                               const char *princ);
+typedef errno_t (*cc_be_remove)(const char *location);
+
+/* A ccache back end */
+struct sss_krb5_cc_be {
+    enum sss_krb5_cc_type type;
+
+    cc_be_create_fn create;
+    cc_be_check_existing check_existing;
+    cc_be_ccache_for_princ ccache_for_princ;
+    cc_be_remove remove;
+};
+
+struct sss_krb5_cc_be file_cc;
+
+errno_t cc_file_create(const char *filename, pcre *illegal_re,
+                       uid_t uid, gid_t gid, bool private_path);
+
+struct sss_krb5_cc_be *get_cc_be_ops(enum sss_krb5_cc_type type);
+struct sss_krb5_cc_be *get_cc_be_ops_ccache(const char *ccache);
+
 char *expand_ccname_template(TALLOC_CTX *mem_ctx, struct krb5child_req *kr,
                              const char *template, bool file_mode,
                              bool case_sensitive, bool *private_path);
 
 errno_t become_user(uid_t uid, gid_t gid);
 
-errno_t create_ccache_dir(TALLOC_CTX *mem_ctx, const char *filename,
-                          pcre *illegal_re, uid_t uid, gid_t gid,
-                          bool private_path);
-
 errno_t get_ccache_file_data(const char *ccache_file, const char *client_name,
                              struct tgt_times *tgtt);
 #endif /* __KRB5_UTILS_H__ */