Mongo doesnt allow periods in usernames

[mr-miles]

We found that the default username template can create invalid usernames which aren't accepted by mongo. Replacing the dots with an allowed character fixes it.

[vishalnayak]

@mr-miles The changes looks good to me. Would you be able to add a test to this effect?

[kalafut]

@pcman312 Any issues with this change? I also wonder if there are other special characters to avoid. Should it be listed in CHANGES?

[mr-miles]

Will attempt to add a test.

SO says the one other restriction on keys is that they can't start with a dollar
https://stackoverflow.com/questions/7975185/mongodb-query-over-a-hash-with-special-chars-in-keys/7976235#7976235

so I think the default template is safe

[pcman312]

This looks good to me. Can you also update the API docs to reflect the updated default template?
https://github.com/hashicorp/vault/blob/master/website/content/api-docs/secret/databases/mongodb.mdx#parameters

Thanks!

[pcman312]

This looks good! What do you think about moving the replace to the end so it only needs to be done once instead of for each of the two fields?

{{ printf "v-%s-%s-%s-%s" (.DisplayName | truncate 15) (.RoleName | truncate 15) (random 20) (unix_time) | replace "." "-" | truncate 100 }}

[mr-miles]

Docs and template updated

[mr-miles]

Test added also

[kalafut]

Thanks for the updates. Can you please add a changelog file to this PR? The /changelog folder has examples.

[mr-miles]

done (and hopefully correctly!)

[vishalnayak]

Thanks for submitting this!