Allow external configuration file

[michaelkrieger]

An external configuration file can be useful:

• For someone that may not wish to modify the original spki file (which can create issues when merging future updates) from the repo in order to configure the app
• If you want to use the spki script for multiple certificates by using a symbolic link for the spki script (or even copying the spki script)

This patch will obey symbolic links, as well as any changes to the name of the script so either of these methods could be used:

    mkdir companyname
    cd companyname
    ln -s ../spki-master/spki spki
    cat << EOF >> spki.conf
    ROOT_DIR='/path/to/data/folder'
    ROOT_CRL_DP=''
    EOF
    ./spki

or

    ln -s spki-master/spki spki-company
    cat << EOF >> spki-company.conf
    ROOT_DIR='/path/to/data/folder'
    ROOT_CRL_DP=''
    EOF
    ./spki-company

and it will override these config settings for when it's run from a script in that folder. This works whether you run it in the current folder or using a relative or absolute path. If the file doesn't exist, it will use the old behaviour.

[kaysond]

I definitely agree this would be a useful feature. But I think using the name of the script file as the config file prefix could be confusing. The config file should have a consistent name, or even be specified directly.

I can think of a few alternative options:

• Add an optional argument (e.g. [--config <file>])
  • requires better options parsing
• Use environment variables to override the variables in the file
  • Use env vars with a prefix a like SPKI_* for specific variables
  • or something like SPKI_CONFIG_FILE to run a file
  • or both
• Search for spki.conf in the working directory and the script directory

In either case, it should definitely be documented in the readme, and a note added in the file itself to indicate the variables could be overwritten.

I'm leaning towards the second one as it seems the most versatile and is a common config practice. Thoughts?

[kaysond]

Implemented via e4bcd95