Add a custom HTTP header in Burp

Quickstart:

If you trust this JAR file:

If you don't trust the jar file (and why should you), instructions on how to compile it are below.

Usage:

After installed, select the "Add Custom Header" tab and pick a regular expression or a hard-coded value as shown below. Keep in mind the regular expression makes sense only when using a macro, so try a hard-coded value first.
The defaults are OK for a JWT-like "Bearer" token
Select Project Options -> Sessions
Add a Session Handling rule
Name it and select "Add", "Invoke a Burp Extension"
Make sure the scope is correct! If you're just trying this out, select 'include all URLs' in the scope (not recommended for regular use).
Select the "Add Bearer Token" option from the list in the following screen

You're now ready to go.

Run this to start a Python webserver on 127.0.0.1:5000:

FLASK_DEBUG=1 FLASK_APP=server.py flask run

The mock webserver will issue a "bearer token" on /login and echo back the bearer token received on /stuff.

See the following screenshots for examples of how to interact with the mock server.

POST to /login:

Using the token when accessing /stuff:

Clone this repo
Burp -> Extender -> APIs
Select "Save interface files" from the bottom of the screen and select a temporary location (e.g. /tmp/foo)
Copy all *.java files into the burp directory containing this repo source:
```
cp /tmp/foo/burp/*.java burpAddCustomHeader/burp/
```

Compile the source:

cd burpAddCustomHeader
mkdir build 
javac -d build burp/BurpExtender.java burp/BurpTab.java

To design the GUI I've used Netbeans. The BurpTab.form file should be enough to recreate it.

LifeProTip: hold the CTRL key when selecting the checkbox in the "Extensions" tab in Burp if you want to re-load an extension.