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Trestle author jinja - output templating support for oscal documents.¤

Unfortunately OSCAL documents are not yet universally accepted. Therefore to support various OSCAL and non-OSCAL compliance workflows trestle author jinja is designed to provide end users with the ability to use jinja to produce customized output. This complements the more structured commands trestle author catalog-{assemble|generate}, trestle author profile-{assemble|generate} and trestle author ssp-{assemble|generate} and allows arbitrary use of jinja.

Jinja and jinja extensions provided by trestle.¤

Jinja is a powerful templating engine that is both more flexible that pure 'Moustache' approaches, and not coupled to a particular web application server (as an example Django templates). Users are encouraged to review the template designer documentation for jinja as all core functionality is exposed.

Trestle's implementation of the Jinja command works in the following way:

  1. The template search space, by default, is relative to the current working directory.
  2. Trestle can inject a lookup table, into the jinja variables to contain booleans / substitutions required by end users using Moustache style variable substitutions.
  3. Trestle can provide a number of interfaces to OSCAL objects, currently a resolved catalog and a SSP, into jinja.
  4. Trestle supports custom jinja tags for importing.
  5. The jinja templating is recursive, to ensure all jinja tags are resolved as appropriate.

More details will be on each of these points below.

CLI invocation¤

Note the examples here use markdown, however, jinja can quite easily target xml or html if used w/o specific markdown content. trestle author jinja -i input_template.md.jinja -o output_file.md -ssp SSP_NAME -p PROFILE_NAME -lut lookup_table.yaml -elp lut.prefix

  • -i input file path, relative to cwd. Users are encouraged to use the file_name.target_extension.jinja best practice as it helps mitigate issues, however is not required.
  • -o final output path, relative to cwd.
  • -ssp (optional) ssp name (in the trestle project). When used the jinja template will have a ssp_md_writer variable exposed to use.
  • -p (optional) profile name (in the trestle project). When used the jinja template will have resolved_catalog and catalog_interface variables to use.
  • -lut (optional) loads yaml into a dictionary in python for which each (top level) variable is available in jinja.
  • -elp (optional) a period separated prefix for the variables in the lookup table. E.g. if the lut contained banana: yellow and the prefix was fruit.tropical using {{ fruit.tropical.banana }} would print out yellow in the jinja template.
  • -pf (optional) use to provide a custom formatting of the substituted parameters in the text. Use dot (.) to indicate where the parameter value will be written. E.g. -pf *.* to italicize all substituted parameters, -pf Prefix:. to add Prefix: to all parameters.

Sample jinja templates¤

Below is a sample jinja template for SSP.

template Description Optional args required
Simple SSP template Sample ssp jinja template which prints out all control responses and includes a front-matter section -ssp and -p for the ssp json and corresponding profile, respectively. Also requires a frontmatter.md file

Variable availability in the jinja template.¤

LUT¤

The lookup table is primarily used for string substitution and to provide variables for basic logic operations in jinja e.g.

The LUT:

names:
  OSCAL: Open Security Compliance Assessment Language
  trestle_pip: compliance-trestle
  trestle_module: trestle
variables:
  mac_os: true

The Jinja template:

Install via pip install {{ names.trestle_pip }} and invoke at the python REPL by import {{ names.trestle_module }}

{% if variables.mac_os %}
Users are recommended to use homebrew to install the latest python 3 and then install python within a venv.
{% endif %}

The output:

Install via pip install compliance-trestle and invoke at the python REPL by import trestle

Users are recommended to use homebrew to install the latest python 3 and then install python within a venv.

Users are free to use the LUT to inject more complex variables (arrays of data etc) to use at their own will using standard jinja templating.

Resolved catalog interface (profile)¤

Passing -p exposes a catalog, resolved from the profile, at catalog and a trestle.core.catalog_interface.CatalogInterface at catalog_interface.

This allows user to perform various task such as iterating ove reach group and printing the group title.

{% for group in catalog_interface.get_all_groups_from_catalog() +%}
## {{ group.title }} {{ group.class }} \({{ group.id|upper }}\)

SSP interface.¤

If -ssp is passed a variable within the jinja template called ssp_md_writer is made available which is an instance of trestle.core.ssp_io.SSPMarkdownWriter. -ssp requires that -p has also been set.

This as allows users, as an example to print out a control response, as markdown

#### What is the solution and how is it implemented?
{{ ssp_md_writer.get_control_response('my_control_id', 3)}}

Custom Jinja tags.¤

Trestle provides custom jinja tags for use specifically with markdown: mdsection_include and md_clean_include.

md_clean_include is similar to the native {% include 'sub_template' %} that jinja provides except for the following:

  1. md_clean_include will look for yaml headers in the markdown content and exclude it from the template
  2. md_clean_include can be used with an optional keyword argument heading_level argument
  3. {% md_clean_include 'path_to_file.md' heading_level=2 %}
  4. The heading level argument adjusts to (based on the number of hashes) the most significant heading in the document, if headings exist.

mdsection_include is similar to the native md_clean_include except that.:

  1. mdsection_include requires an second positional argument which is the title of a heading, from a markdown file, which you want the content from.

  2. E.g: {% mdsection_include 'test_markdown.md' '# Header we want' %}

  3. mdsection_include can be used with an optional keyword argument heading_level argument similar to md_clean_include

  4. {% mdsection_include 'test_markdown.md' '# Header we want' %}

  5. The heading level argument adjusts to (based on the number of hashes) the most significant heading in the chosen section, if headings exist.

md_datestamp inserts a date stamp into the output. By default the date is in the format '%Y-%m-%d', e.g. '2021-12-28' and is followed by a double newline to prevent subsequent headings failing to parse correctly. E.g: {% md_datestamp %} results in a date in the format '2021-12-28' being inserted. md_datestamp can be used with the following optional keyword arguments:

  1. format where a python datetime strftime format string is provided to format the output. E.g. {% md_datestamp format='%B %d, %Y' %} results in December 28, 2021 being inserted.
  2. newline is a boolean to control the addition of a double newline after the inserted date string. For example {% md_datestamp newline=false %} inserts a date in the default format, without additional newlines.

Generate controls as individual markdown pages.¤

Trestle's Jinja functionality allows its users to generate individual markdown pages for each control from a resolved profile catalog. Such functionality can be used later on to pack individual pages into docs of various formats.

When --docs-profile or -dp flag is provided as part of the trestle author jinja command, the provided Jinja template will be used to generate a markdown page for each control in each group.

For example, suppose we would like to generate the markdown page for each control that would contain Control Objective, Control Statement, Expected Evidence, Implementation Guidance and say Table of Parameters used for this control. To achieve that, we can create a simple Jinja template that would be used to generate each page:

# Control Page

{{ control_writer.write_control_with_sections(
   control,
   profile,
   group_title, 
   ['statement', 'objective', 'expected_evidence', 'implementation_guidance', 'table_of_parameters'], 
   {
      'statement':'Control Statement',
      'objective':'Control Objective', 
      'expected_evidence':'Expected Evidence', 
      'implementation_guidance':'Implementation Guidance', 
      'table_of_parameters':'Control Parameters'
   }
   ) 

   | safe
}}

The template above, would call a control writer that would print the required sections (specified in the list) with the provided headers (specified in the dictionary).

We can then generate individual markdown pages by executing: trestle author jinja -i profile_to_docs.md.jinja -o controls -p some_profile -dp

This will create a folder named controls, that would contain a folder per each group and a markdown file per each control in that group. Each markdown file would be formatted using the Jinja template above.

The generated markdown files can then be assembled to the docs of the desired format by adding an indexing page.