[OpenID-Specs-eKYC-IDA] Issue #1337: "evidence_supported" OP metadata shoudl be clarified (openid/ekyc-ida)

[mhainework]

New issue 1337: "evidence_supported" OP metadata shoudl be clarified
https://bitbucket.org/openid/ekyc-ida/issues/1337/evidence_supported-op-metadata-shoudl-be

Mark Haine:

`evidence_supported`: REQUIRED. JSON array containing all types of identity evidence the OP uses. This array MUST have at least one member.

It should be clarified that this should normally only contain members from the list described in section 51.1 evidence Eelment:

* `document`
* `electronic_record`
* `electronic_signature`

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