Support for extensions in Security Schemes

[GiovanniCardamone]

Is there an existing issue that is already proposing this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe it

I am unable to add a security needed

Describe the solution you'd like

would be useful to have the extensions properti in SecuritySchemeObject in order to add extensions to the security

Teachability, documentation, adoption, migration strategy

https://swagger.io/docs/specification/v3_0/openapi-extensions/

What is the motivation / use case for changing the behavior?

would be useful when there are security that requires more than one header

[kamilmysliwiec]

Would you like to create a PR for this issue?