Update index.bs with proposed location extension (#157)

* Update index.bs

* Update index.bs

* Update index.bs

* Update index.bs

index.bs

@@ -1837,7 +1837,53 @@ credential. It is intended primarily for [RPS] that wish to tightly control the
                 82
     </pre>
 
+## Location Extension ## {#uvi-location}
 
+: Extension identifier
+:: `webauthn_loc`
+
+: Client argument
+:: The Boolean value `true` to indicate that this extension is requested by the [RP].
+
+: Client processing
+:: None, except default forwarding of client argument to authenticator argument.
+
+: Authenticator argument
+:: The Boolean value `true`, encoded in CBOR (major type 7, value 21).
+
+: Authenticator processing
+:: If the <a>authenticator</a> does not support the extension, then the authenticator MUST ignore the extension request.  
+    If the <a>authenticator</a> accepts the extension, then the authenticator SHOULD only add this extension data to a packed 
+    attestation or assertion.
+
+: Authenticator data
+:: If the <a>authenticator</a> accepts the extension request, then authenticator data SHOULD provide location data in the form of a 
+    CBOR-encoded map, with the first value being the extension identifier and the second being an array of returned values.  The array 
+    elements SHOULD be derived from (key,value) pairings for each location attribute that the <a>authenticator</a> supports. The following is 
+    an example of authenticator data where the returned array is comprised of a {longitude, latitude, altitude} triplet, following the
+    coordinate representation defined in <a href=https://dev.w3.org/geo/api/spec-source.html#coordinates_interface>The W3C Geolocation API
+    Specification</a>.
+
+    <pre class="highlight">
+        F1 D0                                       -- This is a WebAuthn packed rawData object
+        81                                          -- TUP and ED set
+        00 00 00 01                                 -- (initial) signature counter
+        ...                                         -- all public key alg etc.
+        A1                                          -- extension: CBOR map of one element
+            6C                                      -- Value 1: CBOR text string of 11 bytes
+                77 65 62 61 75 74 68 6E 5F 6C 6F 63 -- "webauthn_loc" UTF-8 string
+            86                                      -- Value 2: array of 6 elements
+                68				    -- Element 1:  CBOR text string of 8 bytes
+                   6C 61 74 69 74 75 64 65          -- “latitude” UTF-8 string
+                FB ...				    -- Element 2:  Latitude as CBOR encoded double-precision float
+                69				    -- Element 3:  CBOR text string of 9 bytes
+                   6C 6F 6E 67 69 74 75 64 65       -- “longitude” UTF-8 string
+                FB ...				    -- Element 4:  Longitude as CBOR encoded double-precision float
+                68				    -- Element 5:  CBOR text string of 8 bytes
+                  61 6C 74 69 74 75 64 65           -- “altitude” UTF-8 string
+                FB ...				    -- Element 6:  Altitude as CBOR encoded double-precision float
+    </pre>
+
 # IANA Considerations # {#iana-considerations}
 
 This specification registers the algorithm names "S256", "S384", "S512", and "SM3" with the IANA JSON Web Algorithms registry as