💡 Enforce localstorage as session storage instead of cookie

[szalonna]

Hello Datadog!

Currently RUM supports local storage as fallback session store when the client runs in an environment which does not meet the requirements for cookie handling and allowFallbackToLocalStorage enabled.

I would love to see an option where we can enforce local storage as session store independently if the platform is available to store a cookie or not.

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Reason

Like mentioned in #590 and #1346 web application security reports mark the session cookie as a low priority finding as it is non-HTTP only. If we, as application developers, could enforce the storage strategy, we could address these findings not by just "ignoring" it. If the fallback strategy works as fine as the cookie one or if there are some known limitations between the two, we should be able to make this decision.

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Possible implementation

• Update InitConfiguration interface with a new flag like enforceToLocalStorage
• Update selectSessionStoreStrategyType to check the enforceToLocalStorage flag before check if platform is able to handle cookies

[BenoitZugmeyer]

Thank you for your feedback. We'll take this into consideration!