User experience with use async_provide_credentials_fn and LazyCachingCredentialsProvider

[Eh2406]

I had a chance to try async_provide_credentials_fn and LazyCachingCredentialsProvider. I may have bean using them wrong, but here is how it went for me. My use case looked like:

async fn get_creds_form_outside_prosses(acc: &str) -> aws_auth::provider::CredentialsResult {
   ...
}
...
for account in accounts {
    let creds = get_creds_form_outside_prosses(&account);
    ....
    let db_config = dynamodb::Config::builder()
        .credentials_provider(
            creds.clone() // the clone is needed because I will also need them for `cw_config`
        ).build();
    let db_client = dynamodb::Client::from_conf(db_config);
    ....
    let cw_config = cloudwatchlogs::Config::builder()
        .credentials_provider(creds)
        .build();
    let cw_client = cloudwatchlogs::Client::from_conf(cw_config);
    ...
}

Now when I am typing this out, I am realizing that somehow (I don't see how) Credentials from a CredentialsResult impls AsyncProvideCredentials. So using it directly works, and is much cleaner then what I tried before!

• Lesson 1: how can we make that more obvious when navigating the code?

Yesterday, I started by looking at AsyncProvideCredentials witch is impled by async_provide_credentials_fn witch has an example in the doc string, so let me try using that.

for account in accounts {
    let creds = async_provide_credentials_fn(|| get_creds_form_outside_prosses(&account));
    ....

error[E0597]: `account` does not live long enough
...
returning this value requires that `account` is borrowed for `'static`
- `account` dropped here (at end of loop) while still borrowed

Why 'static? because .credentials_provider( requires it impl aws_auth::provider::AsyncProvideCredentials + 'static.
I know the arcane trick to get a &'static str! Then I end up needing to add a move

for account in accounts {
    let account = &*Box::leak(account.into_boxed_str());
    let creds = async_provide_credentials_fn(move || get_creds_form_outside_prosses(&account));
    ....

And this is a working solution!

• Lesson 2: Why 'static? How can we make this better?

Some one told me to try LazyCachingCredentialsProvider. So:

for account in accounts {
    let account = &*Box::leak(account.into_boxed_str());
    let creds = LazyCachingCredentialsProvider::builder()
       .refresh(async_provide_credentials_fn(|| get_creds_form_outside_prosses(&account)))
       .build();
    ....

but

no method named `clone` found for struct `LazyCachingCredentialsProvider` in the current scope

• Lesson 3: How do I use LazyCachingCredentialsProvider in more then one config?
• Lesson 4: Is there some way to make a config or client that can be used for different services?

[rcoh]

this extremely helpful. thanks for taking the time to write this up. We're going to take another pass on both the trait as well as write a usage guide: #175.

And for your and other's future context, Credentials implements AsyncProvideCredentials because of a blanket impl on impl AsyncProvideCredentials for T where T: ProvideCredentials

[carllerche]

I'm not sure why you need a Box::leak here. It is the closure that needs to be 'static so it should be sufficient to move an owned String into the closure.

let account = account.to_string();
let creds = async_provide_credentials_fn(move || get_creds_form_outside_prosses(&account));

[Eh2406]

I did try that before posting, and @rcoh tried after I posted, and we could not get it to work. But we may have bean messing things up.

[jdisanti]

I tried it out, and the only way I could get it to compile was to change get_creds_from_outside_process to take the input as an owned String and to also clone it (it complains about not being able to copy String otherwise):

async fn get_creds_from_outside_process(input: String) -> aws_auth::provider::CredentialsResult {
    unimplemented!()
}

fn test() {
    let accounts = vec!["one".to_string(), "two".to_string()];
    for account in accounts {
        let creds =
            async_provide_credentials_fn(move || get_creds_from_outside_process(account.clone()));
    }
}

Any attempt at borrowing the string value resulted in it not living long enough, no matter what permutation I tried.
Definitely seems sub-optimal.