Merge pull request #433 from wunter8/auth-query-param-docs

docs for auth query param

docs/publish.md

@@ -2678,6 +2678,27 @@ Here's a simple example:
     ]));
     ```
 
+#### Auth Query Param
+In some instances, you may want to send auth credentials in the URL (e.g., a GET webhook or a JSON POST request). You
+can use the `auth` query parameter. Set the value to the base64 encoding of the value of the `Authorization` header
+and strip any trailing `=`. **Be sure to only send auth credentials over an HTTPS connection**
+
+Here is an example:
+```
+    Step 1. base64(user:pass)             -> base64(testuser:fakepassword)                    -> dGVzdHVzZXI6ZmFrZXBhc3N3b3Jk
+    Step 2. Authorization header          -> Basic base64(testuser:fakepassword)              -> Basic dGVzdHVzZXI6ZmFrZXBhc3N3b3Jk
+    Step 3. base64(Authorization header)  -> base64(Basic dGVzdHVzZXI6ZmFrZXBhc3N3b3Jk)       -> QmFzaWMgZEdWemRIVnpaWEk2Wm1GclpYQmhjM04zYjNKaw==
+    Step 4. remove trailing `=` (if any)  -> QmFzaWMgZEdWemRIVnpaWEk2Wm1GclpYQmhjM04zYjNKaw== -> QmFzaWMgZEdWemRIVnpaWEk2Wm1GclpYQmhjM04zYjNKaw
+    Step 5. add query param to URL        -> https://ntfy.sh/topic                            -> https://ntfy.sh/topic?auth=QmFzaWMgZEdWemRIVnpaWEk2Wm1GclpYQmhjM04zYjNKaw
+```
+
+!!! note
+    Do NOT remove trailing `=` after step 2
+
+The following command will generate the appropriate value for you on *nix systems:
+
+```echo -n "Basic `echo -n 'testuser:fakepassword' | base64`" | base64 | tr -d '='```
+
 ### Message caching
 !!! info
     If `Cache: no` is used, messages will only be delivered to connected subscribers, and won't be re-delivered if a