improve: HTTP auth display logic and messaging (#4430)

* http-auth: Include unsupported scheme name in error message

* http-auth: Treat authentication scheme case insensitively

The spec refers to RFC 7235 for scheme names, and the RFC says names
are matched case insensitively.

* linter fixes

src/core/plugins/oas3/components/http-auth.jsx

@@ -53,7 +53,7 @@ export default class HttpAuth extends React.Component {
     const Markdown = getComponent( "Markdown" )
     const JumpToPath = getComponent("JumpToPath", true)
 
-    const scheme = schema.get("scheme")
+    const scheme = (schema.get("scheme") || "").toLowerCase()
     let value = this.getValue()
     let errors = errSelectors.allErrors().filter( err => err.get("authId") === name)
 
@@ -125,7 +125,7 @@ export default class HttpAuth extends React.Component {
     )
     }
   return <div>
-    <em><b>{name}</b> HTTP authentication: unsupported or missing scheme</em>
+    <em><b>{name}</b> HTTP authentication: unsupported scheme {`'${scheme}'`}</em>
   </div>
   }
 }