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Think of a scenario where we have a business requirement inside our application where when user tried

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to enter his username or email in the login page, we should not accept any username or email which

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has a word WPEC inside it.

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Of course, I can validate this on the other side also, but I want to validate the back inside so that

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if some authentication fails due to this reason, I can log it or I can write an exception into a database.

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In order to achieve this, we can write a custom filter and inject into the spring security filter change

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flow by using the add filter before method.

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You can see here for your representation purposes.

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I have defined some inbuilt filters like Cotswold, CSR, a filter and the basic authentication filter

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which are provided by spring security framework itself.

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So in this chain of filters, I want to inject my own custom filter, which is of request validation

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filter before the basic authentication filter.

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So whenever we inject our own filter before a certain spring security framework filter, the order we

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will get is just before the number.

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So for our understanding purposes, I just defined class as a filter, which has either one CSR, which

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has other two, followed by my filter, which is arbitrary.

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And at the last we have a filter which is basic authentication filter return order for.

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So in order to achieve this, let's try to go to the backend code and try to implement a filter with

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the logic that we have discussed.

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So here I have implemented a filter, which I'll explain you now.

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But don't worry if you really want to check what I have written inside this filter, you can always

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download the source code from the summary of the section and explore astbury.

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What needs, as you can see, the very first requirement that we have to follow is we have to implement

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the filter from the package Java X dot.

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So let inside this we need to override the method to filter and it receives three parameters request,

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response and filters.

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Since we want to deal with the filters, we have to convert that request whatever we result into the

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history to pisolite request.

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Once we convert that here.

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What I I'm trying to see is during the initial authentication from the UI in the intercept that we have

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written, we are sending an header with the name Attribution and with the base64 encoding with both

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email and the password separated by a column.

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So this is what is happening from the UI.

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So similarly on the backend, in order to understand what is the email entered by the user, I read

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through the header with the name Attribution and inside the header.

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If the header starts with the name Basic, which means this is my proper header where I can find my

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email and password, I can decode it using base64 encoding and decoding.

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Once I have the decoded string, I will separate the string using a delimiter that we have used Colen

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in the UI and the very first string that I get from this token is Imon.

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And inside the email I'm just checking if I how inside it.

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If it is there, then I will generate a response which indicates that request received to the UI.

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So this is not a four zero one.

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It just indicates I received an invalid email to the UI application.

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So this we want to execute before actual authentication happens.

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Due to that reason, we injected this filter just before the basic authentication filter.

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Now let's try to configure this custom filter inside our application for the same.

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You have to come to project security config Java.

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And here this is the line that I have added to configure a filter.

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We can add this line anywhere inside this matter.

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But I just added before our the matches and here I am saying you have to add filter before and parsing

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my own custom filter by initializing it, followed by what is a spring security filter I want to consider

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in order to inject my filter just before it's the filter that we want to consider is basic authentication

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filter from the spring security framework.

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IT with this configuration, we inject our own custom filter into the spring security filter chain and

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let's try to start the application by going to the main class.

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Why debugging and Java application from the login page, let's try to form a proper login, which is

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happy aderet example dot com one, two, three, four, five and clicking Sinem to login.

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Successful as we expected, but let's try to check the console of the back and see whether our filter

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is really added into the spring security filter change.

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As you can see here just before basic authentication filter our Walkerston filter, which is request

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validation before filter has been added to the filter change.

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And since our e-mail is valid, it didn't show any error.

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Let us try to log out and this time I will enter.

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AP straight example, dot com two, three, four, five is the password.

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We keep a breakpoint in our filter for your reference.

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Clicking, signing.

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I can see here the breakpoint has been stopped here and this is the token that we send username colon

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and the password and the way we decoded it and fetching the only email pad.

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And clearly my email contains now it satisfies a condition that I have written, so it will return a

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four hundred error, which indicates bad request to the UI, but it will not call the extra filter in

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the chain because I am returning from this filter itself to the client and you can see here in the console,

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my request has been filled with the reason for hundred that will return and that back in this way we

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can define our one custom filter and added this to before whatever we define filter provided by the

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spring security framework in the next, will you let us try to add a filter after an inbuilt filter

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provided by spring security?

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Thank you.

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And see you in the next room by.