clarification - 4.1.2 Secure transaction API details

[vgalindo]

In the sentence :
'use cases are not highly sensitive in terms of transaction context confidentiality, which means that standard SOP rules are considered sufficient without any need for end-to-end encryption (like secure messaging).'

--> 2 remarks
The CG should wonder is we want to have this API being operated only in the context of Priviledged Context [https://www.w3.org/TR/secure-contexts/] or not.
In addition, the usage of 'secure messaging', looks very smart card centric and does not refer to the ususal working in W3C specifications (HTTPS, for ex).

[sbahloul]

To be reviewed today

[sbahloul]

Add in 6. TODO