New method: GetSecuredApiKeyRemainingValidity

[Ant-hem]

Summary

When a secured API keys expire, search breaks. The current workaround is more complex
than it needs to be.

The options for developers using Algolia require, at every place where a search
operation is performed, catching an operation error, identify it as a
"ValidUntil" error, then regenerate the API key, and perform the search
operation again.

The idea is to define a method which tells if a SecuredAPIKey
is expired or not without making a single call to Algolia's API.

References

• Specs: https://github.com/algolia/algoliasearch-client-specs-internal/pull/25

[Haroenv]

Is it an option to have a method getSecuredApiKeyValidity(key), so a person can do their own calculation, and this method can be side-effect free?

[Haroenv]

Note that decoding from base64 is different in browser (atob) than in Node (using Buffer)

Browser:

const decoded = atob(key);

Node:

const decoded = Buffer.from(key, 'base64').toString();

Buffer.from will have to be polyfilled for Node.js < 6 https://yarnpkg.com/en/package/buffer-from

Buffer.from can be "progressively enhanced":

const decoded =
  Buffer.from && Buffer.from !== Uint8Array.from
    ? Buffer.from(key, 'base64').toString()
    : new Buffer(key, 'base64').toString();