def linkAccount()

in plugin-oauth2/plugin/grails-app/controllers/grails/plugin/springsecurity/oauth2/SpringSecurityOAuth2Controller.groovy [160:197]
38 lines of code
9 McCabe index (conditional complexity)

    def linkAccount(OAuth2LinkAccountCommand command) {
        OAuth2SpringToken oAuth2SpringToken = session[SPRING_SECURITY_OAUTH_TOKEN] as OAuth2SpringToken
        if (!oAuth2SpringToken) {
            log.warn "linkAccount: OAuthToken not found in session"
            throw new OAuth2Exception('Authentication error')
        }
        if (request.post) {
            if (!springSecurityOauth2BaseService.authenticationIsValid(command.username, command.password)) {
                log.info "Authentication error for use ${command.username}"
                command.errors.rejectValue("username", "OAuthLinkAccountCommand.authentication.error")
                render view: 'ask', model: [linkAccountCommand: command]
                return
            }
            def commandValid = command.validate()
            def User = springSecurityOauth2BaseService.lookupUserClass()
            boolean linked = commandValid && User.withTransaction { status ->
                def user = User.findByUsername(command.username)
                if (user) {
                    user.addTooAuthIDs(provider: oAuth2SpringToken.providerName, accessToken: oAuth2SpringToken.socialId, user: user)
                    if (user.validate() && user.save()) {
                        oAuth2SpringToken = springSecurityOauth2BaseService.updateOAuthToken(oAuth2SpringToken, user)
                        return true
                    } else {
                        return false
                    }
                } else {
                    command.errors.rejectValue("username", "OAuthLinkAccountCommand.username.not.exists")
                }
                status.setRollbackOnly()
                return false
            }
            if (linked) {
                authenticateAndRedirect(oAuth2SpringToken, getDefaultTargetUrl())
                return
            }
        }
        render view: 'ask', model: [linkAccountCommand: command]
    }