This is the query:
string(//user[username/text()='input' and password/text()='input']/account/text())
And we also can see this table:
Members Username | Email | Account type —– | —– | —— Steve | steve@jobs.com | subscriber John | John@doe.org | administrator Eric | ric@ard.biz | subscriber
So, we’ll give this payload ' or username='John' or ' and the full query will be:
username=' or username='John' or '&password=a

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