add slides lecture 17

lectures/revealjs/17-rest-api.adoc

+= REST APIs 
+:customcss: slides.css
+:icons: font
+:includedir: revealjs/includes/
+:LECTURE_TOPIC: REST APIs 
+:LECTURE_NO: 17th Lecture
+
+include::{includedir}header.adoc[]
+
+[.smaller-80][.center-paragraph]
+IT1901 Fall 2020 - {LECTURE_NO}
+
+[.smaller-80]
+== Overview
+
+- REST APIs
+** HTTP requests
+** Methods
+** APIs
+** REST Recap
+
+
+
+== HTTP requests
+ - **H**yper**t**ext **T**ransfer **P**rotocol (HTTP)
+ - clients (e.g. browser) send requests
+ - servers (web site / service) send responses
+
+== HTTP Request message
+ 
+ - a request line `GET / HTTP/1.1`
+ - request headers - `User-Agent`, `Accept`, `Content-Type` etc.
+ - an empty line (containing only a `carriage return` and a `line feed`)
+ - an optional message body
+
+== HTTP Methods
+
+- HTTP specification defines `methods` to indicate what action is expected from the server
+** GET, HEAD, OPTIONS
+** POST, PUT, PATCH
+** DELETE
+
+== APIs
+
+- **A**pplication **P**rogramming **I**nterface
+- "Glue" that makes possible different pieces of software to interoperate
+- It is meant to be machine readable / usable
+- APIs are everywhere - at different levels - software libraries, operating system, applications, web services etc.
+
+== APIs (2) 
+
+- typically a set of calls or requests, expected call format, expected response format, data structures
+- separate the implementation from the interface
+- allow programs in one language to use functionality written in some other language
+- cater to modular software
+
+[background-color = "#124990"]
+[color = "#fff6d5"]
+== REST
+
+[.smaller-80]
+== REST
+- **RE**presentational **S**tate **T**ransfer (REST)  
+- architectural style involving use of Web Services 
+- set of constraints are applied 
+** client server
+** statelessness (no client context is stored on the server side)
+** cacheability (responses state if they can be cached or not)
+** uniform interface
+** layered system (adding layers like proxy or load balancer)
+
+
+== REST (cont.)
+
+- Web services that implement REST are called RESTful APIs
+- a base URI, example: https://gitlab.stud.idi.ntnu.no/api/v4
+- set of exposed web resources
+- standard HTTP methods (e.g., GET, POST, PUT, PATCH and DELETE);
+- data formats for requests and responses (json, xml, etc)
+
+== !
+
+image::../images/lecture12/rtodo.png[canvas, size=contain]
+
+== Security considerations
+
+- CORS (Cross-Origin Resource Sharing)
+** headers `Access-Control-Allow-Origin` 
+- Authentication (Basic Auth,  OAuth etc)
+- HTTPS (HTTP over TLS)
+
+
+[background-color = "#124990"]
+[color = "#fff6d5"]
+== Summary
+
+include::{includedir}footer.adoc[]
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