Is there a "Best Practice" process for handling external forms (non-Marketo type login forms) so that Marketo can still cookie them?
While, as Jim said, Marketo-hosted forms do not directly set cookies -- there are in fact situations in which Forms 2.0 actions are *intended* to set the Munchkin cookie, but the underlying code is buggy -- this may not be what you're asking.
If you wish an external form submission to associate the Munchkin session with a known lead instead of remaining anonymous, you have three approaches:
1. Submit a hidden Marketo form alongside your external form (recommended, easiest)
2. Call the Munchkin API associateLead method (more programmer-y, requires a developer though quite easy if you have one)
3. Use REST or SOAP API methods (not recommended unless you can prove beyond a reasonable doubt that 1. and 2. are unattainable in your environment, which is unlikely)
Forms don't cookie leads. Munchkin does. If you have Munchkin on your external pages, you should be okay in regards to cookies.
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