This is the list of the standard apache2 modules that are compiled into the Debian apache2 binary: core, http_core, prefork/worker/perchild, mod_access, mod_auth, mod_log_config, mod_logio, mod_env, mod_setenvif, mod_mime, mod_status, mod_autoindex, mod_negotiation, mod_dir, mod_alias, mod_so.
You can check what modules are built statically in the apache2 binary, by running the command:
apache2 -l Compiled in modules: core.c mod_access.c mod_auth.c mod_log_config.c mod_logio.c mod_env.c mod_setenvif.c worker.c http_core.c mod_mime.c mod_status.c mod_autoindex.c mod_negotiation.c mod_dir.c mod_alias.c mod_so.c
Here is a short description and the link to the apache docs for each of the modules from above:
core, http_core: Core Apache HTTP Server features that are always available prefork/worker/perchild: The MPM module (based on the actual MPM installed) mod_access: Provides access control based on client hostname, IP address, or other characteristics of the client request. mod_auth: User authentication using text files mod_log_config: Logging of the requests made to the server mod_logio: Logging of input and output bytes per request mod_env: Modifies the environment which is passed to CGI scripts and SSI pages mod_setenvif: Allows the setting of environment variables based on characteristics of the request mod_mime: Associates the requested filename’s extensions with the file’s behavior (handlers and filters) and content (mime-type, language, character set and encoding) mod_status: Provides information on server activity and performance mod_autoindex: Generates directory indexes, automatically, similar to the Unix ls command or the Win32 dir shell command mod_negotiation: Provides for content negotiation mod_dir: Provides for “trailing slash” redirects and serving directory index files mod_alias: Provides for mapping different parts of the host filesystem in the document tree and for URL redirection mod_so: Loading of executable code and modules into the server at start-up or restart time