[Openid-specs-ab] Issue #1566: Add credential type to OP Metadata (openid/connect)

[David Chadwick]

New issue 1566: Add credential type to OP Metadata
https://bitbucket.org/openid/connect/issues/1566/add-credential-type-to-op-metadata

David Chadwick:

Currently each credential in the credentials\_supported set does not specify the type of credential that it applies to. This has a number of disadvantages:

* wallets do not have a globally unambiguous identifier for the credential \(which the type is\)
* to counteract the above, the credential key is recommended to be collision resistant. Adding the type to the definition will mean that the key only needs to be locally unique, as it simply becomes the name of the JSON object in the metadata definition.
* the way that the metadata for ISO mdl credentials and W3C verifiable credentials is specified is not uniform. \(e.g. there is a namespace parameter that is only applicable to mDL metadata, which can be removed once the type is added\)
* wallets that want to display the type of credential to the user do not have a way of being informed how to display this

By introducting the type parameter as the first parameter of each credential in the credentias\_supported object, and making this the unique URL for each specific type of credential, we can clearly state at the start of the metadata which type of credential this metadata applies to. So for example, for mdl the type could be http://standards.iso.org/18013-5.2019, for a W3C Verifiable Credential \(of any type\) it would be https://www.w3.org/2018/credentials#VerifiableCredential.

Because a credential can be of multiple types then the type parameter will be a set of values.

The display qualifier will indicate to the wallet how this \(type of\) credential should be displayed to the user.