plugins {
    compile ":oauth:2.6.1"
}

oauth {
    providers {
        facebook {
            api = org.scribe.builder.api.FacebookApi
            key = '你的Facebook应用ID'
            secret = '你的Facebook应用密钥'
            callback = "${grails.serverURL}/oauth/facebook/callback"
            scope = 'email,public_profile' // 请求的权限范围
        }
    }
}

class OAuthController {
    def oauthService
    
    def facebook() {
        if (!params.code) {
            // 第一步：重定向到Facebook授权页面
            def redirectUrl = oauthService.authenticate('facebook')
            redirect(url: redirectUrl)
        } else {
            // 第二步：处理回调，获取访问令牌
            def token = oauthService.getAccessToken('facebook', params)
            
            if (token) {
                // 第三步：使用令牌获取用户信息
                def facebookResource = oauthService.getFacebookResource(token, 'me?fields=id,name,email,picture')
                def profile = parseProfile(facebookResource)
                
                // 处理获取到的用户信息
                session.user = profile
                redirect(controller: 'user', action: 'welcome')
            } else {
                flash.error = "Failed to authenticate with Facebook"
                redirect(controller: 'auth', action: 'login')
            }
        }
    }
    
    private def parseProfile(String json) {
        def jsonSlurper = new groovy.json.JsonSlurper()
        def result = jsonSlurper.parseText(json)
        
        return [
            id: result.id,
            name: result.name,
            email: result.email,
            picture: result.picture?.data?.url
        ]
    }
}

<g:link controller="oauth" action="facebook">Login with Facebook</g:link>