Add provider validation

Author: marcoscaceres

index.html

@@ -567,6 +567,42 @@ <h3>
       </li>
       <li>If |requests| is empty, [=exception/throw=] a {{TypeError}}.
       </li>
+      <li>If |providers| [=list/is empty=], [=exception/throw=] a
+      {{TypeError}}.
+      </li>
+      <li>Let |range| be [=list/get the indices|the indices=] of |providers|.
+      </li>
+      <li>[=Set/For each=] |n| of the |range|:
+        <ol>
+          <li>Let |provider| be the [=list/item=] at |providers|'s |n| index.
+          </li>
+          <li>If |provider|'s {{DigitalCredentialGetRequest/protocol}} is not
+          allowed by the user agent, [=exception/throw=] a
+          {{NotSupportedError}} {{DOMException}}.
+          </li>
+          <li>If the [=digital credential/exchange protocol=] defines an IDL
+          [=dictionary=] for [=converted to an idl value|conversion=]:
+            <ol>
+              <li>Let |request| be |provider|'s
+              {{DigitalCredentialGetRequest/data}} [=converted to an idl
+              value|converted=] to a |dictionary|. [=exception/throw|Rethrow=]
+              any exceptions.
+              </li>
+            </ol>
+          </li>
+          <li>Otherwise, let |request| be |provider|'s
+          {{DigitalCredentialGetRequest/data}}.
+          </li>
+          <li>Validate |request| against any validation rules set forth in the
+          corresponding [=digital credentials registry/specification=]. If any
+          of |request|'s members are invalid, [=exception/throw=] a
+          {{TypeError}}.
+          </li>
+          <li>Set [=list/item=] at |providers|'s |n| index's
+          {{DigitalCredentialGetRequest/data}} to |request|.
+          </li>
+        </ol>
+      </li>
       <li>
         <aside class="issue">
           Details of how to actually get the [=digital credential=] are