json_extractor | Pull objects out of a JSON file | Serialization library

If you want to store the accessToken value into a JMeter property for using in other Thread Group(s) be aware that properties are global for the whole JVM and remain until JMeter is restarted so if you define a single accessToken property - each JMeter Thread (or iteration) will overwrite the value.

The solution is to use current thread (or iteration) number as prefix or postfix, this can be done using either __${__threadNum} function or relevant JMeter Variable depending on how iteration is defined or both.

Example setup:

1. In first thread group: ${__setProperty(access_token_${__threadNum},bar,)}
2. In second thread group: ${__P(access_token_${__threadNum},)}

Demo:

If you want to save the values into a file writing into the current one is not the best idea as you can (and most probably will) get malformed file due to a form of a race condition. So I would recommend using Sample Variables property instead.

If you add the next line to user.properties file:

sample_variables=email,password,accessToken

JMeter will store the variables named ${email}, ${password}, and ${accessToken} along with their values in the .jtl results file which is basically CSV file which can be re-used anywhere else.

However if you have a requirement to store only the credentials and the token you can go for the Flexible File Writer plugin and configure it to save the aforementioned variables values into a separate file, the relevant configuration would be as simple as:

How can I modify what I am doing in order to be able to yield from multiple coroutines in parallel?

You need a function that merges two async sequences into one, iterating over both in parallel and yielding elements from one or the other, as they become available. While such a function is not included in the current standard library, you can find one in the aiostream package.

You can also write your own merge function, as shown in this answer: