Updating the feature extraction analyzer documentation (google#2973)

* Update the feature extraction analyzer documentation

data/winevt_features.yaml

@@ -47,7 +47,7 @@
 # For more details and examples of such an extraction check the Timesketch
 # documentation:
 #
-# TODO(Add documentation link)
+# https://timesketch.org/guides/analyzers/feature_extraction/
 #
 # ------------------------------------------------------------------------
 # 4624: An account was successfully logged on.

docs/guides/analyzers/feature_extraction.md

@@ -2,22 +2,41 @@
 hide:
   - footer
 ---
-The feature extraction analyzer creates attributes out of event data based on regular expressions. Different
-features can be specified in the `data/regex_features.yaml` file.
+The feature extraction analyzer creates attributes out of event data based on
+different extraction plugins.
 
-Please be aware that this analyzer does *not* extract ipv4, email-addresses and similar from *all* events, but only those that match the query_string.
+Currently supported:
+* Regular expression based extractions
+  * [Regex Extraction Plugin](#regex-extraction-plugin)
+* Plaso parsed windows event logs
+  * [Winevt Extraction Plugin](#winevt-extraction-plugin)
+
+> **Note**
+Please be aware that this analyzer does *not* extract ipv4, email addresses and
+similar from *all* events, but only those that match the definitions configured
+for the plugins explained below!
 
 ### Use case
 
-This analyzer is helpful to built a list of `email_addresses` in a sketch that are used in in `WEBHIST`. To do that, run the analyzer to have the feature extracted. Check the results by running a query: `email_address:*`.
+This analyzer is helpful to extract additional data from events as separate
+attributes. Those extracted attributes can then be used in search, lookups,
+correlations, aggregations or with analyzers.
+
+For example: In the default configuration, the analyzer will extract
+`email_addresses` from the message field of events with the source `WEBHIST`
+matching the regular expression.
 
-Those results now can be used in an aggregation to plot a table limited to that column.
+## Regex Extraction Plugin
 
-Another way of extracting that information is via API, querying events that contain `email_address:*` as a pandas dataframe, and work from there.
+This feature extraction plugin uses regular expression to extract matching
+strings from an existing event attribute (e.g. message) and adds it as a new
+attribute to the event.
 
 ### Configuration
 
-A feature extraction definition looks like this:
+Features are defined in [data/regex_features.yaml](../../../data/regex_features.yaml)
+
+A regex based feature extraction definition looks like this:
 
 ```
 name:
@@ -40,9 +59,9 @@ name:
        keep_multimatch: False
 ```
 
-Each definition needs to define either a query_string or a query_dsl.
+Each definition needs to define either a `query_string` or a `query_dsl`.
 
-`re_flags` is a list of flags as strings from the re module. These include:
+`re_flags` is a list of flags as strings from the `re` module. These include:
 - DEBUG
 - DOTALL
 - IGNORECASE
@@ -72,3 +91,68 @@ The feature extraction works in the way that the query is run, and the regular e
 The first value extracted is then stored inside the "store_as" attribute.
 If there are emojis or tags defined they are also applied to that event.
 In the end, if a view is supposed to be created a view searching for the added tag is added (only if there are results).
+
+## Winevt Extraction Plugin
+
+This feature extraction plugin uses configured mappings to create new attributes
+for Windows Event Log events that were parsed using [Plaso](https://github.com/log2timeline/plaso).
+
+The mapping is based on the `strings` array, that gets generated by Plaso for
+the event data entries.
+
+> **Note**
+The winevt extraction plugin does *not* map all Windows Event Log fields. It
+does only map the ones configured in [data/winevt_features.yaml](../../../data/winevt_features.yaml)!
+
+### Configuration
+
+Features are defined in [data/winevt_features.yaml](../../../data/winevt_features.yaml)
+
+A mapping for a Windows Event uses the yaml format and looks like this:
+
+```
+name:
+
+    source_name:            Type: list[str] | REQUIRED | case-insensitive
+                            A list of source names to match against. Multiple
+                            entries will be checked with OR.
+
+    provider_identifier:    Type: list[str] | OPTIONAL | case-insensitive
+                            A list of provider identifiers to match against.
+                            Multiple entries will be checked with OR.
+
+    event_version:          Type: int | REQUIRED
+                            The event version to match against.
+
+    event_identifier:       Type: int | REQUIRED
+                            The event identifier to match against.
+
+    references:             Type: list[str] | OPTIONAL
+                            A list of references to provide as context and
+                            source for the event mapping. E.g. a URL to the
+                            official Microsoft documentation on the event.
+
+    mapping:                Type: list[dict] | REQUIRED
+                            A list of dicts that define the new attribute name
+                            and the string index of the event to extract the
+                            value from. Additonally it can also contain an
+                            alias list to add multiple attributes with
+                            the same value but different names.
+
+        name:               Type: str | REQUIRED
+                            The name of the new attribute to create.
+
+        string_index:       Type: int | REQUIRED | Starting at index 0
+                            The string index of the event to extract the
+                            value from. Based on the plaso extracted "strings"
+                            attribute with Windows eventlog entries.
+
+        aliases:            Type: list[str] | OPTIONAL
+                            A list of aliases to add additionally to the
+                            offical name of the attribute. This can be used
+                            to add different field names matching individual
+                            field name ontologies. E.g. srcIP, domain, etc.
+```
+
+Checkout the preconfigured mappings for some examples:
+[data/winevt_features.yaml](../../../data/winevt_features.yaml)