public class LicenseActivationController {
    ...
    public static Boolean CheckValidLicense(String activationId, String username, String password) {
        ...
    }
}

<apex:page standardController="Contact" extensions="LicenseActivationController">
    <apex:form >
        <apex:pageBlock title="License Activation">
            <apex:pageBlockSection columns="1">
                <apex:outputLabel value="Username:" for="username"/>
                <apex:inputText value="{!username}" id="username" />
                <apex:outputLabel value="Password:" for="password"/>
                <apex:inputText value="{!password}" id="password" />
                <apex:outputLabel value="Activation ID:" for="activationID"/>
                <apex:inputText value="{!activationID}" id="activationID" />
            </apex:pageBlockSection>
            <apex:pageBlockButtons >
                <apex:commandButton value="Activate" />
            </apex:pageBlockButtons>
        </apex:pageBlock>
    </apex:form>
</apex:page>