Manual:$wgAutoCreateTempUser

Details
Configuration for automatic creation of temporary accounts on page save. This can be enabled to avoid exposing the IP addresses of casual editors who do not explicitly create an account.

An associative array with the following keys:
 * : (bool) Whether auto-creation is enabled.
 * : (array) A list of actions for which the feature is enabled. Currently only  is supported.
 * : (string) The pattern used when generating new usernames. This should have  indicating the place where the serial string will be substituted.
 * : (string) The pattern used when determining whether a username is a temporary user. This affects the rights of the user and also prevents explicit creation of users with matching names. This is ignored if  is false.
 * : (string) A pattern used to determine whether a username should be denied for explicit creation, in addition to matchPattern. This is used even if  is false.
 * : (array) Configuration for generation of unique integer indexes which are used to make temporary usernames.
 * : (string) May be "local" to allocate indexes using the local database. If the CentralAuth extension is enabled, it may be "centralauth". Extensions may plug in additional types using the attribute.
 * (int, default 1): A small integer. This can be set to a value greater than 1 to avoid acquiring a global lock when allocating IDs, at the expense of making the IDs be non-monotonic.
 * : (array) Configuration for mapping integer indexes to strings to substitute into.
 * : (string) May be
 * to use ASCII decimal numbers
 * to use numbers localized using a specific language
 * to use numbers in an arbitrary base between 2 and 36, with an optional list of "bad" IDs to skip over.
 * : to use ASCII decimal numbers that are short but non-consecutive.
 * : (string) With, the language code
 * : (int) With, the base
 * : (array) With, an array with the bad unmapped indexes in the values. The integers must be sorted and the list must never change after the indexes have been allocated. The keys must be zero-based array indexes.
 * : (bool) With, whether to use uppercase letters, default false.