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Excerpts from Andrew Plunk's message of 2013-11-07 06:48:33 +0800:
> Hello All,
> 
> Imagine for a minute that you are displaying outputs from heat, but some of those outputs could have sensitive data (think passwords or private keys). It would be beneficial to allow outputs to be accessed once, and then go into a locked state. This could result in the following:
> 

This is an interesting concept. I'd like to start with a problem
statement though, as it is not clear what this is meant to solve.

> 1). After an output is accessed for the first time, the output will become locked, and subsequent calls to the engine to return that output will return nothing.
> example:
> >show stack 
> 
> "outputs": {
>   "password": "password"
>  }
> 
> >show stack
> 
> "outputs": {
> }
> 
> 
> 2). Another option is after an output is accessed for the first time, the output will become locked, and subsequent calls to the engine will return the output with a flag saying that this output has been locked, allowing whatever is consuming that output to take the necessary action.
> example:
> 
> >show stack
> 
> "outputs": {
>   "password": {
>     "value": "password",
>     "locked": false
>   }
> }
> 
> >show stack
> 
> "outputs": {
>   "password": {
>     "value": "password",
>     "locked": true
>   }
> }
> 
> 
> The outputs section of the template for either case would could look like:
> outputs:
>   password:
>     value: { get_attr: [ some_resource, some_value ] }
>     description: The password
>     view_once: True
> 

So it seems that the problem you are seeking to solve is limiting access
to sensitive outputs. The solution mentioned above certainly narrows
the attack surface, but it suffers from a DOS race condition where a
bad actor can lock you out of your own resource.

I have a different idea for that, which is to encrypt the output using
public key cryptography.

heat stack-create -f mytemplate.yaml -P PasswordRecipientKey="$(gpg
--armor --print-key me at foo.com)"

And then have an output type of "Encrypted"

Outputs:
  Password:
    Type: Encrypted
    Keys:
      - {Ref: PasswordRecipientKey}

Now you can simply decrypt this with your local gpg key. heatclient
could even automatically do this for you making it transparent as long
as you have a gpg key agent running.