Custom authentication for Modules (#11659)

This change adds new module callbacks that can override the default password based authentication associated with ACLs. With this, Modules can register auth callbacks through which they can implement their own Authentication logic. When `AUTH` and `HELLO AUTH ...` commands are used, Module based authentication is attempted and then normal password based authentication is attempted if needed.
The new Module APIs added in this PR are - `RM_RegisterCustomAuthCallback` and `RM_BlockClientOnAuth` and `RedisModule_ACLAddLogEntryByUserName `.

Module based authentication will be attempted for all Redis users (created through the ACL SETUSER cmd or through Module APIs) even if the Redis user does not exist at the time of the command. This gives a chance for the Module to create the RedisModule user and then authenticate via the RedisModule API - from the custom auth callback.

For the AUTH command, we will support both variations - `AUTH <username> <password>` and `AUTH <password>`. In case of the `AUTH <password>` variation, the custom auth callbacks are triggered with “default” as the username and password as what is provided.


### RedisModule_RegisterCustomAuthCallback
```
void RM_RegisterCustomAuthCallback(RedisModuleCtx *ctx, RedisModuleCustomAuthCallback cb) {
```
This API registers a callback to execute to prior to normal password based authentication. Multiple callbacks can be registered across different modules. These callbacks are responsible for either handling the authentication, each authenticating the user or explicitly denying, or deferring it to other authentication mechanisms. Callbacks are triggered in the order they were registered. When a Module is unloaded, all the auth callbacks registered by it are unregistered. The callbacks are attempted, in the order of most recently registered callbacks, when the AUTH/HELLO (with AUTH field is provided) commands are called. The callbacks will be called with a module context along with a username and a password, and are expected to take one of the following actions:

 (1) Authenticate - Use the RM_Authenticate* API successfully and return `REDISMODULE_AUTH_HANDLED`. This will immediately end the auth chain as successful and add the OK reply.
(2) Block a client on authentication - Use the `RM_BlockClientOnAuth` API and return `REDISMODULE_AUTH_HANDLED`. Here, the client will be blocked until the `RM_UnblockClient `API is used which will trigger the auth reply callback (provided earlier through the `RM_BlockClientOnAuth`). In this reply callback, the Module should authenticate, deny or skip handling authentication.
(3) Deny Authentication - Return `REDISMODULE_AUTH_HANDLED` without authenticating or blocking the client. Optionally, `err` can be set to a custom error message. This will immediately end the auth chain as unsuccessful and add the ERR reply.
(4) Skip handling Authentication - Return `REDISMODULE_AUTH_NOT_HANDLED` without blocking the client. This will allow the engine to attempt the next custom auth callback.

If none of the callbacks authenticate or deny auth, then password based auth is attempted and will authenticate or add failure logs and reply to the clients accordingly.

### RedisModule_BlockClientOnAuth
```
RedisModuleBlockedClient *RM_BlockClientOnAuth(RedisModuleCtx *ctx, RedisModuleCustomAuthCallback reply_callback,
                                               void (*free_privdata)(RedisModuleCtx*,void*))
```
This API can only be used from a Module from the custom auth callback. If a client is not in the middle of custom module based authentication, ERROR is returned. Otherwise, the client is blocked and the `RedisModule_BlockedClient` is returned similar to the `RedisModule_BlockClient` API.

### RedisModule_ACLAddLogEntryByUserName
```
int RM_ACLAddLogEntryByUserName(RedisModuleCtx *ctx, RedisModuleString *username, RedisModuleString *object, RedisModuleACLLogEntryReason reason)
```
Adds a new entry in the ACL log with the `username` RedisModuleString provided. This simplifies the Module usage because now, developers do not need to create a Module User just to add an error ACL Log entry. Aside from accepting username (RedisModuleString) instead of a RedisModuleUser, it is the same as the existing `RedisModule_ACLAddLogEntry` API.


### Breaking changes
- HELLO command - Clients can now only set the client name and RESP protocol from the `HELLO` command if they are authenticated. Also, we now finish command arg validation first and return early with a ERR reply if any arg is invalid. This is to avoid mutating the client name / RESP from a command that would have failed on invalid arguments.

### Notable behaviors
- Module unblocking - Now, we will not allow Modules to block the client from inside the context of a reply callback (triggered from the Module unblock flow `moduleHandleBlockedClients`).

---------

Co-authored-by: Madelyn Olson <34459052+madolson@users.noreply.github.com>

1 files changed, 297 insertions, 71 deletions

diff --git a/src/module.c b/src/module.c
index 418c5bd32..6ce57f69c 100644
--- a/src/module.c
+++ b/src/module.c
@@ -229,6 +229,7 @@ struct RedisModuleKey {
  * a Redis module. */
 struct RedisModuleBlockedClient;
 typedef int (*RedisModuleCmdFunc) (RedisModuleCtx *ctx, void **argv, int argc);
+typedef int (*RedisModuleAuthCallback)(RedisModuleCtx *ctx, void *username, void *password, RedisModuleString **err);
 typedef void (*RedisModuleDisconnectFunc) (RedisModuleCtx *ctx, struct RedisModuleBlockedClient *bc);
 
 /* This struct holds the information about a command registered by a module.*/
@@ -249,6 +250,12 @@ typedef struct RedisModuleCommand RedisModuleCommand;
  * only the type, proto and protolen are filled. */
 typedef struct CallReply RedisModuleCallReply;
 
+/* Structure to hold the module auth callback & the Module implementing it. */
+typedef struct RedisModuleAuthCtx {
+    struct RedisModule *module;
+    RedisModuleAuthCallback auth_cb;
+} RedisModuleAuthCtx;
+
 /* Structure representing a blocked client. We get a pointer to such
  * an object when blocking from modules. */
 typedef struct RedisModuleBlockedClient {
@@ -256,6 +263,8 @@ typedef struct RedisModuleBlockedClient {
                         was destroyed during the life of this object. */
     RedisModule *module;    /* Module blocking the client. */
     RedisModuleCmdFunc reply_callback; /* Reply callback on normal completion.*/
+    RedisModuleAuthCallback auth_reply_cb; /* Reply callback on completing blocking
+                                                    module authentication. */
     RedisModuleCmdFunc timeout_callback; /* Reply callback on timeout. */
     RedisModuleDisconnectFunc disconnect_callback; /* Called on disconnection.*/
     void (*free_privdata)(RedisModuleCtx*,void*);/* privdata cleanup callback.*/
@@ -274,6 +283,11 @@ typedef struct RedisModuleBlockedClient {
                                      Used for measuring latency of blocking cmds */
 } RedisModuleBlockedClient;
 
+/* This is a list of Module Auth Contexts. Each time a Module registers a callback, a new ctx is
+ * added to this list. Multiple modules can register auth callbacks and the same Module can have
+ * multiple auth callbacks. */
+static list *moduleAuthCallbacks;
+
 static pthread_mutex_t moduleUnblockedClientsMutex = PTHREAD_MUTEX_INITIALIZER;
 static list *moduleUnblockedClients;
 
@@ -3521,7 +3535,7 @@ int RM_SetClientNameById(uint64_t id, RedisModuleString *name) {
         errno = ENOENT;
         return REDISMODULE_ERR;
     }
-    if (clientSetName(client, name) == C_ERR) {
+    if (clientSetName(client, name, NULL) == C_ERR) {
         errno = EINVAL;
         return REDISMODULE_ERR;
     }
@@ -7369,6 +7383,7 @@ void unblockClientFromModule(client *c) {
  *
  */
 RedisModuleBlockedClient *moduleBlockClient(RedisModuleCtx *ctx, RedisModuleCmdFunc reply_callback,
+                                            RedisModuleAuthCallback auth_reply_callback,
                                             RedisModuleCmdFunc timeout_callback, void (*free_privdata)(RedisModuleCtx*,void*),
                                             long long timeout_ms, RedisModuleString **keys, int numkeys, void *privdata,
                                             int flags) {
@@ -7388,6 +7403,7 @@ RedisModuleBlockedClient *moduleBlockClient(RedisModuleCtx *ctx, RedisModuleCmdF
     bc->client = (islua || ismulti) ? NULL : c;
     bc->module = ctx->module;
     bc->reply_callback = reply_callback;
+    bc->auth_reply_cb = auth_reply_callback;
     bc->timeout_callback = timeout_callback;
     bc->disconnect_callback = NULL; /* Set by RM_SetDisconnectCallback() */
     bc->free_privdata = free_privdata;
@@ -7408,6 +7424,13 @@ RedisModuleBlockedClient *moduleBlockClient(RedisModuleCtx *ctx, RedisModuleCmdF
         addReplyError(c, islua ?
             "Blocking module command called from Lua script" :
             "Blocking module command called from transaction");
+    } else if (ctx->flags & REDISMODULE_CTX_BLOCKED_REPLY) {
+        c->bstate.module_blocked_handle = NULL;
+        addReplyError(c, "Blocking module command called from a Reply callback context");
+    }
+    else if (!auth_reply_callback && clientHasModuleAuthInProgress(c)) {
+        c->bstate.module_blocked_handle = NULL;
+        addReplyError(c, "Clients undergoing module based authentication can only be blocked on auth");
     } else {
         if (keys) {
             blockForKeys(c,BLOCKED_MODULE,keys,numkeys,timeout,flags&REDISMODULE_BLOCK_UNBLOCK_DELETED);
@@ -7418,6 +7441,185 @@ RedisModuleBlockedClient *moduleBlockClient(RedisModuleCtx *ctx, RedisModuleCmdF
     return bc;
 }
 
+/* This API registers a callback to execute in addition to normal password based authentication.
+ * Multiple callbacks can be registered across different modules. When a Module is unloaded, all the
+ * auth callbacks registered by it are unregistered.
+ * The callbacks are attempted (in the order of most recently registered first) when the AUTH/HELLO
+ * (with AUTH field provided) commands are called.
+ * The callbacks will be called with a module context along with a username and a password, and are
+ * expected to take one of the following actions:
+ * (1) Authenticate - Use the RM_AuthenticateClient* API and return REDISMODULE_AUTH_HANDLED.
+ * This will immediately end the auth chain as successful and add the OK reply.
+ * (2) Deny Authentication - Return REDISMODULE_AUTH_HANDLED without authenticating or blocking the
+ * client. Optionally, `err` can be set to a custom error message and `err` will be automatically
+ * freed by the server.
+ * This will immediately end the auth chain as unsuccessful and add the ERR reply.
+ * (3) Block a client on authentication - Use the RM_BlockClientOnAuth API and return
+ * REDISMODULE_AUTH_HANDLED. Here, the client will be blocked until the RM_UnblockClient API is used
+ * which will trigger the auth reply callback (provided through the RM_BlockClientOnAuth).
+ * In this reply callback, the Module should authenticate, deny or skip handling authentication.
+ * (4) Skip handling Authentication - Return REDISMODULE_AUTH_NOT_HANDLED without blocking the
+ * client. This will allow the engine to attempt the next module auth callback.
+ * If none of the callbacks authenticate or deny auth, then password based auth is attempted and
+ * will authenticate or add failure logs and reply to the clients accordingly.
+ *
+ * Note: If a client is disconnected while it was in the middle of blocking module auth, that
+ * occurrence of the AUTH or HELLO command will not be tracked in the INFO command stats.
+ *
+ * The following is an example of how non-blocking module based authentication can be used:
+ *
+ *      int auth_cb(RedisModuleCtx *ctx, RedisModuleString *username, RedisModuleString *password, RedisModuleString **err) {
+ *          const char *user = RedisModule_StringPtrLen(username, NULL);
+ *          const char *pwd = RedisModule_StringPtrLen(password, NULL);
+ *          if (!strcmp(user,"foo") && !strcmp(pwd,"valid_password")) {
+ *              RedisModule_AuthenticateClientWithACLUser(ctx, "foo", 3, NULL, NULL, NULL);
+ *              return REDISMODULE_AUTH_HANDLED;
+ *          }
+ *
+ *          else if (!strcmp(user,"foo") && !strcmp(pwd,"wrong_password")) {
+ *              RedisModuleString *log = RedisModule_CreateString(ctx, "Module Auth", 11);
+ *              RedisModule_ACLAddLogEntryByUserName(ctx, username, log, REDISMODULE_ACL_LOG_AUTH);
+ *              RedisModule_FreeString(ctx, log);
+ *              const char *err_msg = "Auth denied by Misc Module.";
+ *              *err = RedisModule_CreateString(ctx, err_msg, strlen(err_msg));
+ *              return REDISMODULE_AUTH_HANDLED;
+ *          }
+ *          return REDISMODULE_AUTH_NOT_HANDLED;
+ *       }
+ *
+ *      int RedisModule_OnLoad(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+ *          if (RedisModule_Init(ctx,"authmodule",1,REDISMODULE_APIVER_1)== REDISMODULE_ERR)
+ *              return REDISMODULE_ERR;
+ *          RedisModule_RegisterAuthCallback(ctx, auth_cb);
+ *          return REDISMODULE_OK;
+ *      }
+ */
+void RM_RegisterAuthCallback(RedisModuleCtx *ctx, RedisModuleAuthCallback cb) {
+    RedisModuleAuthCtx *auth_ctx = zmalloc(sizeof(RedisModuleAuthCtx));
+    auth_ctx->module = ctx->module;
+    auth_ctx->auth_cb = cb;
+    listAddNodeHead(moduleAuthCallbacks, auth_ctx);
+}
+
+/* Helper function to invoke the free private data callback of a Module blocked client. */
+void moduleInvokeFreePrivDataCallback(client *c, RedisModuleBlockedClient *bc) {
+    if (bc->privdata && bc->free_privdata) {
+        RedisModuleCtx ctx;
+        int ctx_flags = c == NULL ? REDISMODULE_CTX_BLOCKED_DISCONNECTED : REDISMODULE_CTX_NONE;
+        moduleCreateContext(&ctx, bc->module, ctx_flags);
+        ctx.blocked_privdata = bc->privdata;
+        ctx.client = bc->client;
+        bc->free_privdata(&ctx,bc->privdata);
+        moduleFreeContext(&ctx);
+    }
+}
+
+/* Unregisters all the module auth callbacks that have been registered by this Module. */
+void moduleUnregisterAuthCBs(RedisModule *module) {
+    listIter li;
+    listNode *ln;
+    listRewind(moduleAuthCallbacks, &li);
+    while ((ln = listNext(&li))) {
+        RedisModuleAuthCtx *ctx = listNodeValue(ln);
+        if (ctx->module == module) {
+            listDelNode(moduleAuthCallbacks, ln);
+            zfree(ctx);
+        }
+    }
+}
+
+/* Search for & attempt next module auth callback after skipping the ones already attempted.
+ * Returns the result of the module auth callback. */
+int attemptNextAuthCb(client *c, robj *username, robj *password, robj **err) {
+    int handle_next_callback = c->module_auth_ctx == NULL;
+    RedisModuleAuthCtx *cur_auth_ctx = NULL;
+    listNode *ln;
+    listIter li;
+    listRewind(moduleAuthCallbacks, &li);
+    int result = REDISMODULE_AUTH_NOT_HANDLED;
+    while((ln = listNext(&li))) {
+        cur_auth_ctx = listNodeValue(ln);
+        /* Skip over the previously attempted auth contexts. */
+        if (!handle_next_callback) {
+            handle_next_callback = cur_auth_ctx == c->module_auth_ctx;
+            continue;
+        }
+        /* Remove the module auth complete flag before we attempt the next cb. */
+        c->flags &= ~CLIENT_MODULE_AUTH_HAS_RESULT;
+        RedisModuleCtx ctx;
+        moduleCreateContext(&ctx, cur_auth_ctx->module, REDISMODULE_CTX_NONE);
+        ctx.client = c;
+        *err = NULL;
+        c->module_auth_ctx = cur_auth_ctx;
+        result = cur_auth_ctx->auth_cb(&ctx, username, password, err);
+        moduleFreeContext(&ctx);
+        if (result == REDISMODULE_AUTH_HANDLED) break;
+        /* If Auth was not handled (allowed/denied/blocked) by the Module, try the next auth cb. */
+    }
+    return result;
+}
+
+/* Helper function to handle a reprocessed unblocked auth client.
+ * Returns REDISMODULE_AUTH_NOT_HANDLED if the client was not reprocessed after a blocking module
+ * auth operation.
+ * Otherwise, we attempt the auth reply callback & the free priv data callback, update fields and
+ * return the result of the reply callback. */
+int attemptBlockedAuthReplyCallback(client *c, robj *username, robj *password, robj **err) {
+    int result = REDISMODULE_AUTH_NOT_HANDLED;
+    if (!c->module_blocked_client) return result;
+    RedisModuleBlockedClient *bc = (RedisModuleBlockedClient *) c->module_blocked_client;
+    bc->client = c;
+    if (bc->auth_reply_cb) {
+        RedisModuleCtx ctx;
+        moduleCreateContext(&ctx, bc->module, REDISMODULE_CTX_BLOCKED_REPLY);
+        ctx.blocked_privdata = bc->privdata;
+        ctx.blocked_ready_key = NULL;
+        ctx.client = bc->client;
+        ctx.blocked_client = bc;
+        result = bc->auth_reply_cb(&ctx, username, password, err);
+        moduleFreeContext(&ctx);
+    }
+    moduleInvokeFreePrivDataCallback(c, bc);
+    c->module_blocked_client = NULL;
+    c->lastcmd->microseconds += bc->background_duration;
+    bc->module->blocked_clients--;
+    zfree(bc);
+    return result;
+}
+
+/* Helper function to attempt Module based authentication through module auth callbacks.
+ * Here, the Module is expected to authenticate the client using the RedisModule APIs and to add ACL
+ * logs in case of errors.
+ * Returns one of the following codes:
+ * AUTH_OK - Indicates that a module handled and authenticated the client.
+ * AUTH_ERR - Indicates that a module handled and denied authentication for this client.
+ * AUTH_NOT_HANDLED - Indicates that authentication was not handled by any Module and that
+ * normal password based authentication can be attempted next.
+ * AUTH_BLOCKED - Indicates module authentication is in progress through a blocking implementation.
+ * In this case, authentication is handled here again after the client is unblocked / reprocessed. */
+int checkModuleAuthentication(client *c, robj *username, robj *password, robj **err) {
+    if (!listLength(moduleAuthCallbacks)) return AUTH_NOT_HANDLED;
+    int result = attemptBlockedAuthReplyCallback(c, username, password, err);
+    if (result == REDISMODULE_AUTH_NOT_HANDLED) {
+        result = attemptNextAuthCb(c, username, password, err);
+    }
+    if (c->flags & CLIENT_BLOCKED) {
+        /* Modules are expected to return REDISMODULE_AUTH_HANDLED when blocking clients. */
+        serverAssert(result == REDISMODULE_AUTH_HANDLED);
+        return AUTH_BLOCKED;
+    }
+    c->module_auth_ctx = NULL;
+    if (result == REDISMODULE_AUTH_NOT_HANDLED) {
+        c->flags &= ~CLIENT_MODULE_AUTH_HAS_RESULT;
+        return AUTH_NOT_HANDLED;
+    }
+    if (c->flags & CLIENT_MODULE_AUTH_HAS_RESULT) {
+        c->flags &= ~CLIENT_MODULE_AUTH_HAS_RESULT;
+        if (c->authenticated) return AUTH_OK;
+    }
+    return AUTH_ERR;
+}
+
 /* This function is called from module.c in order to check if a module
  * blocked for BLOCKED_MODULE and subtype 'on keys' (bc->blocked_on_keys true)
  * can really be unblocked, since the module was able to serve the client.
@@ -7488,7 +7690,24 @@ int moduleTryServeClientBlockedOnKey(client *c, robj *key) {
 RedisModuleBlockedClient *RM_BlockClient(RedisModuleCtx *ctx, RedisModuleCmdFunc reply_callback,
                                          RedisModuleCmdFunc timeout_callback, void (*free_privdata)(RedisModuleCtx*,void*),
                                          long long timeout_ms) {
-    return moduleBlockClient(ctx,reply_callback,timeout_callback,free_privdata,timeout_ms, NULL,0,NULL,0);
+    return moduleBlockClient(ctx,reply_callback,NULL,timeout_callback,free_privdata,timeout_ms, NULL,0,NULL,0);
+}
+
+/* Block the current client for module authentication in the background. If module auth is not in
+ * progress on the client, the API returns NULL. Otherwise, the client is blocked and the RM_BlockedClient
+ * is returned similar to the RM_BlockClient API.
+ * Note: Only use this API from the context of a module auth callback. */
+RedisModuleBlockedClient *RM_BlockClientOnAuth(RedisModuleCtx *ctx, RedisModuleAuthCallback reply_callback,
+                                               void (*free_privdata)(RedisModuleCtx*,void*)) {
+    if (!clientHasModuleAuthInProgress(ctx->client)) {
+        addReplyError(ctx->client, "Module blocking client on auth when not currently undergoing module authentication");
+        return NULL;
+    }
+    RedisModuleBlockedClient *bc = moduleBlockClient(ctx,NULL,reply_callback,NULL,free_privdata,0, NULL,0,NULL,0);
+    if (ctx->client->flags & CLIENT_BLOCKED) {
+        ctx->client->flags |= CLIENT_PENDING_COMMAND;
+    }
+    return bc;
 }
 
 /* This call is similar to RedisModule_BlockClient(), however in this case we
@@ -7552,7 +7771,7 @@ RedisModuleBlockedClient *RM_BlockClient(RedisModuleCtx *ctx, RedisModuleCmdFunc
 RedisModuleBlockedClient *RM_BlockClientOnKeys(RedisModuleCtx *ctx, RedisModuleCmdFunc reply_callback,
                                                RedisModuleCmdFunc timeout_callback, void (*free_privdata)(RedisModuleCtx*,void*),
                                                long long timeout_ms, RedisModuleString **keys, int numkeys, void *privdata) {
-    return moduleBlockClient(ctx,reply_callback,timeout_callback,free_privdata,timeout_ms, keys,numkeys,privdata,0);
+    return moduleBlockClient(ctx,reply_callback,NULL,timeout_callback,free_privdata,timeout_ms, keys,numkeys,privdata,0);
 }
 
 /* Same as RedisModule_BlockClientOnKeys, but can take REDISMODULE_BLOCK_* flags
@@ -7568,7 +7787,7 @@ RedisModuleBlockedClient *RM_BlockClientOnKeysWithFlags(RedisModuleCtx *ctx, Red
                                                         RedisModuleCmdFunc timeout_callback, void (*free_privdata)(RedisModuleCtx*,void*),
                                                         long long timeout_ms, RedisModuleString **keys, int numkeys, void *privdata,
                                                         int flags) {
-    return moduleBlockClient(ctx,reply_callback,timeout_callback,free_privdata,timeout_ms, keys,numkeys,privdata,flags);
+    return moduleBlockClient(ctx,reply_callback,NULL,timeout_callback,free_privdata,timeout_ms, keys,numkeys,privdata,flags);
 }
 
 /* This function is used in order to potentially unblock a client blocked
@@ -7643,6 +7862,7 @@ int RM_UnblockClient(RedisModuleBlockedClient *bc, void *privdata) {
 int RM_AbortBlock(RedisModuleBlockedClient *bc) {
     bc->reply_callback = NULL;
     bc->disconnect_callback = NULL;
+    bc->auth_reply_cb = NULL;
     return RM_UnblockClient(bc,NULL);
 }
 
@@ -7709,16 +7929,13 @@ void moduleHandleBlockedClients(void) {
             reply_us = elapsedUs(replyTimer);
             moduleFreeContext(&ctx);
         }
-
-        /* Free privdata if any. */
-        if (bc->privdata && bc->free_privdata) {
-            RedisModuleCtx ctx;
-            int ctx_flags = c == NULL ? REDISMODULE_CTX_BLOCKED_DISCONNECTED : REDISMODULE_CTX_NONE;
-            moduleCreateContext(&ctx, bc->module, ctx_flags);
-            ctx.blocked_privdata = bc->privdata;
-            ctx.client = bc->client;
-            bc->free_privdata(&ctx,bc->privdata);
-            moduleFreeContext(&ctx);
+        /* Hold onto the blocked client if module auth is in progress. The reply callback is invoked
+         * when the client is reprocessed. */
+        if (c && clientHasModuleAuthInProgress(c)) {
+            c->module_blocked_client = bc;
+        } else {
+            /* Free privdata if any. */
+            moduleInvokeFreePrivDataCallback(c, bc);
         }
 
         /* It is possible that this blocked client object accumulated
@@ -7733,7 +7950,7 @@ void moduleHandleBlockedClients(void) {
          * This needs to be out of the reply callback above given that a
          * module might not define any callback and still do blocking ops.
          */
-        if (c && !bc->blocked_on_keys) {
+        if (c && !clientHasModuleAuthInProgress(c) && !bc->blocked_on_keys) {
             updateStatsOnUnblock(c, bc->background_duration, reply_us, server.stat_total_error_replies != prev_error_replies);
         }
 
@@ -7746,7 +7963,7 @@ void moduleHandleBlockedClients(void) {
             /* Put the client in the list of clients that need to write
              * if there are pending replies here. This is needed since
              * during a non blocking command the client may receive output. */
-            if (clientHasPendingReplies(c) &&
+            if (!clientHasModuleAuthInProgress(c) && clientHasPendingReplies(c) &&
                 !(c->flags & CLIENT_PENDING_WRITE))
             {
                 c->flags |= CLIENT_PENDING_WRITE;
@@ -7757,8 +7974,10 @@ void moduleHandleBlockedClients(void) {
         /* Free 'bc' only after unblocking the client, since it is
          * referenced in the client blocking context, and must be valid
          * when calling unblockClient(). */
-        bc->module->blocked_clients--;
-        zfree(bc);
+        if (!(c && clientHasModuleAuthInProgress(c))) {
+            bc->module->blocked_clients--;
+            zfree(bc);
+        }
 
         /* Lock again before to iterate the loop. */
         pthread_mutex_lock(&moduleUnblockedClientsMutex);
@@ -9135,24 +9354,41 @@ int RM_ACLCheckChannelPermissions(RedisModuleUser *user, RedisModuleString *ch,
     return REDISMODULE_OK;
 }
 
-/* Adds a new entry in the ACL log.
- * Returns REDISMODULE_OK on success and REDISMODULE_ERR on error.
- *
- * For more information about ACL log, please refer to https://redis.io/commands/acl-log */
-int RM_ACLAddLogEntry(RedisModuleCtx *ctx, RedisModuleUser *user, RedisModuleString *object, RedisModuleACLLogEntryReason reason) {
-    int acl_reason;
+/* Helper function to map a RedisModuleACLLogEntryReason to ACL Log entry reason. */
+int moduleGetACLLogEntryReason(RedisModuleACLLogEntryReason reason) {
+    int acl_reason = 0;
     switch (reason) {
         case REDISMODULE_ACL_LOG_AUTH: acl_reason = ACL_DENIED_AUTH; break;
         case REDISMODULE_ACL_LOG_KEY: acl_reason = ACL_DENIED_KEY; break;
         case REDISMODULE_ACL_LOG_CHANNEL: acl_reason = ACL_DENIED_CHANNEL; break;
         case REDISMODULE_ACL_LOG_CMD: acl_reason = ACL_DENIED_CMD; break;
-        default: return REDISMODULE_ERR;
+        default: break;
     }
+    return acl_reason;
+}
 
+/* Adds a new entry in the ACL log.
+ * Returns REDISMODULE_OK on success and REDISMODULE_ERR on error.
+ *
+ * For more information about ACL log, please refer to https://redis.io/commands/acl-log */
+int RM_ACLAddLogEntry(RedisModuleCtx *ctx, RedisModuleUser *user, RedisModuleString *object, RedisModuleACLLogEntryReason reason) {
+    int acl_reason = moduleGetACLLogEntryReason(reason);
+    if (!acl_reason) return REDISMODULE_ERR;
     addACLLogEntry(ctx->client, acl_reason, ACL_LOG_CTX_MODULE, -1, user->user->name, sdsdup(object->ptr));
     return REDISMODULE_OK;
 }
 
+/* Adds a new entry in the ACL log with the `username` RedisModuleString provided.
+ * Returns REDISMODULE_OK on success and REDISMODULE_ERR on error.
+ *
+ * For more information about ACL log, please refer to https://redis.io/commands/acl-log */
+int RM_ACLAddLogEntryByUserName(RedisModuleCtx *ctx, RedisModuleString *username, RedisModuleString *object, RedisModuleACLLogEntryReason reason) {
+    int acl_reason = moduleGetACLLogEntryReason(reason);
+    if (!acl_reason) return REDISMODULE_ERR;
+    addACLLogEntry(ctx->client, acl_reason, ACL_LOG_CTX_MODULE, -1, username->ptr, sdsdup(object->ptr));
+    return REDISMODULE_OK;
+}
+
 /* Authenticate the client associated with the context with
  * the provided user. Returns REDISMODULE_OK on success and
  * REDISMODULE_ERR on error.
@@ -9188,6 +9424,10 @@ static int authenticateClientWithUser(RedisModuleCtx *ctx, user *user, RedisModu
     ctx->client->user = user;
     ctx->client->authenticated = 1;
 
+    if (clientHasModuleAuthInProgress(ctx->client)) {
+        ctx->client->flags |= CLIENT_MODULE_AUTH_HAS_RESULT;
+    }
+
     if (callback) {
         ctx->client->auth_callback = callback;
         ctx->client->auth_callback_privdata = privdata;
@@ -11278,6 +11518,7 @@ void moduleInitModulesSystem(void) {
     server.loadmodule_queue = listCreate();
     server.module_configs_queue = dictCreate(&sdsKeyValueHashDictType);
     modules = dictCreate(&modulesDictType);
+    moduleAuthCallbacks = listCreate();
 
     /* Set up the keyspace notification subscriber list and static client */
     moduleKeyspaceSubscribers = listCreate();
@@ -11582,6 +11823,7 @@ int moduleLoad(const char *path, void **module_argv, int module_argc, int is_loa
             moduleUnregisterSharedAPI(ctx.module);
             moduleUnregisterUsedAPI(ctx.module);
             moduleRemoveConfigs(ctx.module);
+            moduleUnregisterAuthCBs(ctx.module);
             moduleFreeModuleStructure(ctx.module);
         }
         moduleFreeContext(&ctx);
@@ -11604,16 +11846,21 @@ int moduleLoad(const char *path, void **module_argv, int module_argc, int is_loa
 
     serverLog(LL_NOTICE,"Module '%s' loaded from %s",ctx.module->name,path);
 
+    int post_load_err = 0;
     if (listLength(ctx.module->module_configs) && !ctx.module->configs_initialized) {
         serverLogRaw(LL_WARNING, "Module Configurations were not set, likely a missing LoadConfigs call. Unloading the module.");
-        moduleUnload(ctx.module->name);
-        moduleFreeContext(&ctx);
-        return C_ERR;
+        post_load_err = 1;
     }
 
     if (is_loadex && dictSize(server.module_configs_queue)) {
         serverLogRaw(LL_WARNING, "Loadex configurations were not applied, likely due to invalid arguments. Unloading the module.");
-        moduleUnload(ctx.module->name);
+        post_load_err = 1;
+    }
+
+    if (post_load_err) {
+        /* Unregister module auth callbacks (if any exist) that this Module registered onload. */
+        moduleUnregisterAuthCBs(ctx.module);
+        moduleUnload(ctx.module->name, NULL);
         moduleFreeContext(&ctx);
         return C_ERR;
     }
@@ -11628,32 +11875,29 @@ int moduleLoad(const char *path, void **module_argv, int module_argc, int is_loa
 }
 
 /* Unload the module registered with the specified name. On success
- * C_OK is returned, otherwise C_ERR is returned and errno is set
- * to the following values depending on the type of error:
- *
- * * ENONET: No such module having the specified name.
- * * EBUSY: The module exports a new data type and can only be reloaded. 
- * * EPERM: The module exports APIs which are used by other module. 
- * * EAGAIN: The module has blocked clients. 
- * * EINPROGRESS: The module holds timer not fired.
- * * ECANCELED: Unload module error.  */
-int moduleUnload(sds name) {
+ * C_OK is returned, otherwise C_ERR is returned and errmsg is set
+ * with an appropriate message. */
+int moduleUnload(sds name, const char **errmsg) {
     struct RedisModule *module = dictFetchValue(modules,name);
 
     if (module == NULL) {
-        errno = ENOENT;
+        *errmsg = "no such module with that name";
         return C_ERR;
     } else if (listLength(module->types)) {
-        errno = EBUSY;
+        *errmsg = "the module exports one or more module-side data "
+                  "types, can't unload";
         return C_ERR;
     } else if (listLength(module->usedby)) {
-        errno = EPERM;
+        *errmsg = "the module exports APIs used by other modules. "
+                  "Please unload them first and try again";
         return C_ERR;
     } else if (module->blocked_clients) {
-        errno = EAGAIN;
+        *errmsg = "the module has blocked clients. "
+                  "Please wait for them to be unblocked and try again";
         return C_ERR;
     } else if (moduleHoldsTimer(module)) {
-        errno = EINPROGRESS;
+        *errmsg = "the module holds timer that is not fired. "
+                  "Please stop the timer or wait until it fires.";
         return C_ERR;
     }
 
@@ -11678,6 +11922,7 @@ int moduleUnload(sds name) {
     moduleUnregisterSharedAPI(module);
     moduleUnregisterUsedAPI(module);
     moduleUnregisterFilters(module);
+    moduleUnregisterAuthCBs(module);
     moduleRemoveConfigs(module);
 
     /* Remove any notification subscribers this module might have */
@@ -12301,35 +12546,13 @@ NULL
         }
 
     } else if (!strcasecmp(subcmd,"unload") && c->argc == 3) {
-        if (moduleUnload(c->argv[2]->ptr) == C_OK)
+        const char *errmsg = NULL;
+        if (moduleUnload(c->argv[2]->ptr, &errmsg) == C_OK)
             addReply(c,shared.ok);
         else {
-            char *errmsg;
-            switch(errno) {
-            case ENOENT:
-                errmsg = "no such module with that name";
-                break;
-            case EBUSY:
-                errmsg = "the module exports one or more module-side data "
-                         "types, can't unload";
-                break;
-            case EPERM:
-                errmsg = "the module exports APIs used by other modules. "
-                         "Please unload them first and try again";
-                break;
-            case EAGAIN:
-                errmsg = "the module has blocked clients. "
-                         "Please wait them unblocked and try again";
-                break;
-            case EINPROGRESS:
-                errmsg = "the module holds timer that is not fired. "
-                         "Please stop the timer or wait until it fires.";
-                break;
-            default:
-                errmsg = "operation not possible.";
-                break;
-            }
-            addReplyErrorFormat(c,"Error unloading module: %s",errmsg);
+            if (errmsg == NULL) errmsg = "operation not possible.";
+            addReplyErrorFormat(c, "Error unloading module: %s", errmsg);
+            serverLog(LL_WARNING, "Error unloading module %s: %s", (sds) c->argv[2]->ptr, errmsg);
         }
     } else if (!strcasecmp(subcmd,"list") && c->argc == 2) {
         addReplyLoadedModules(c);
@@ -12978,6 +13201,7 @@ void moduleRegisterCoreAPI(void) {
     REGISTER_API(GetKeyNameFromDigest);
     REGISTER_API(GetDbIdFromDigest);
     REGISTER_API(BlockClient);
+    REGISTER_API(BlockClientOnAuth);
     REGISTER_API(UnblockClient);
     REGISTER_API(IsBlockedReplyRequest);
     REGISTER_API(IsBlockedTimeoutRequest);
@@ -13104,6 +13328,7 @@ void moduleRegisterCoreAPI(void) {
     REGISTER_API(ACLCheckKeyPermissions);
     REGISTER_API(ACLCheckChannelPermissions);
     REGISTER_API(ACLAddLogEntry);
+    REGISTER_API(ACLAddLogEntryByUserName);
     REGISTER_API(FreeModuleUser);
     REGISTER_API(DeauthenticateAndCloseClient);
     REGISTER_API(AuthenticateClientWithACLUser);
@@ -13134,4 +13359,5 @@ void moduleRegisterCoreAPI(void) {
     REGISTER_API(RegisterStringConfig);
     REGISTER_API(RegisterEnumConfig);
     REGISTER_API(LoadConfigs);
+    REGISTER_API(RegisterAuthCallback);
 }