Add basic auth with writekey auth

Author: Niall Brennan

src/connections/sources/catalog/libraries/server/http-api/index.md

@@ -11,12 +11,34 @@ Segment has native [sources](/docs/connections/sources/) for most use cases (lik
 
 ### Authentication
 
-Choose between [writeKey authentication](#writeKey-authentication) and [OAuth](#oauth) to authenticate requests. 
+Choose between [writeKey authentication](#writeKey-authentication), [basic authentication](#basic-authentication) and [OAuth](#oauth) to authenticate requests. 
 
 #### writeKey authentication
 Authenticate to the Tracking API by sending your project's **Write Key** along with a request.
 The authentication writeKey should be sent as part of the body of the request. This will be encrypted over https.
 
+```
+  curl --location 'https://api.segment.io/v1/track' \
+  --header 'Content-Type: application/json' \
+  --data-raw '{
+      "event": "happy-path-a3ef8a6f-0482-4694-bc4d-4afba03a0eab",
+      "email": "test@example.org",
+      "userId": "123",
+      "writeKey": "sx1dTUoxt8oErcWt1S1H23IZnr9SSRhy"
+  }'
+```
+
+> info ""
+> For this auth type, you do not need to set any authentication header. 
+
+#### Basic authentication
+Basic authentication uses HTTP Basic Auth, which involves a `username:password` that is base64 encoded and prepended with the string `Basic`.
+
+In practice that means taking a Segment source **Write Key**,`'abc123'`, as the username, adding a colon, and then the password field is left empty. After base64 encoding `'abc123:'` becomes `'YWJjMTIzOg=='`; and this is passed in the authorization header like so: `'Authorization: Basic YWJjMTIzOg=='`.
+
+> info ""
+> Include a colon before encoding. While encoding the write key without a colon might work due to backward compatibility, this won't always be the case.  
+
 #### OAuth
 [Obtain the access token](/docs/connections/oauth/) from the Authorization Server specific to the region.