docs: add readme

Author: TomokiMiyauci

README.md

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+# authorization-parser
+
+[![deno land](http://img.shields.io/badge/available%20on-deno.land/x-lightgrey.svg?logo=deno)](https://deno.land/x/authorization_parser)
+[![deno doc](https://doc.deno.land/badge.svg)](https://doc.deno.land/https/deno.land/x/authorization_parser/mod.ts)
+[![GitHub release (latest by date)](https://img.shields.io/github/v/release/httpland/authorization-parser)](https://github.com/httpland/authorization-parser/releases)
+[![codecov](https://codecov.io/github/httpland/authorization-parser/branch/main/graph/badge.svg)](https://codecov.io/gh/httpland/authorization-parser)
+[![GitHub](https://img.shields.io/github/license/httpland/authorization-parser)](https://github.com/httpland/authorization-parser/blob/main/LICENSE)
+
+[![test](https://github.com/httpland/authorization-parser/actions/workflows/test.yaml/badge.svg)](https://github.com/httpland/authorization-parser/actions/workflows/test.yaml)
+[![NPM](https://nodei.co/npm/@httpland/authorization-parser.png?mini=true)](https://nodei.co/npm/@httpland/authorization-parser/)
+
+HTTP `Authorization` field parser and serializer.
+
+Compliant with
+[RFC 9110, 11.6.2. Authorization](https://www.rfc-editor.org/rfc/rfc9110.html#section-11.6.2).
+
+## Parsing
+
+Parse string into [Authorization](#authorization).
+
+```ts
+import { parseAuthorization } from "https://deno.land/x/authorization_parser@$VERSION/parse.ts";
+import { assertEquals } from "https://deno.land/std/testing/asserts.ts";
+
+const result = parseAuthorization("Basic token68");
+
+assertEquals(parseAuthorization("Basic token68"), {
+  authScheme: "Basic",
+  token: "token68",
+});
+assertEquals(
+  parseAuthorization(`Bearer realm="example", error="invalid_token"`),
+  {
+    authScheme: "Bearer",
+    token: {
+      realm: `"example"`,
+      error: `"invalid_token"`,
+    },
+  },
+);
+```
+
+### Throwing error
+
+In the following cases, throws an error.
+
+- Syntax error
+- Semantic error
+
+#### Syntax error
+
+If field value has an invalid syntax, it may throw a `SyntaxError`.
+
+The syntax follows
+[Authorization ABNF](https://www.rfc-editor.org/rfc/rfc9110.html#section-11.6.2-2).
+
+```ts
+import { parseAuthorization } from "https://deno.land/x/authorization_parser@$VERSION/parse.ts";
+import { assertThrows } from "https://deno.land/std/testing/asserts.ts";
+
+assertThrows(() => parseAuthorization("<invalid>"));
+```
+
+#### Semantic error
+
+In case of semantic errors, throw an `Error`.
+
+- If there is a duplicate key(case insensitive) in
+  [auth-param](https://www.rfc-editor.org/rfc/rfc9110.html#section-11.2-5)
+
+```ts
+import { parseAuthorization } from "https://deno.land/x/authorization_parser@$VERSION/parse.ts";
+import { assertThrows } from "https://deno.land/std/testing/asserts.ts";
+
+assertThrows(() =>
+  parseAuthorization("scheme duplicate=value, Duplicate=value")
+);
+```
+
+## Authorization
+
+`Authorization` is following structure:
+
+| Name       | Type                                       | Description            |
+| ---------- | ------------------------------------------ | ---------------------- |
+| authScheme | `string`                                   | Authentication scheme. |
+| token      | `Token68` &#124; `AuthParam` &#124; `null` | token68 or auth-param. |
+
+### Token68
+
+It is the same as `string`.
+
+The token68 syntax allows the 66 unreserved URI characters, plus a few others,
+so that it can hold a base64, base64url (URL and filename safe alphabet),
+base32, or base16 (hex) encoding, with or without padding, but excluding
+whitespace.
+
+### AuthParam
+
+It is name/value pairs.
+
+```ts
+interface AuthParam {
+  readonly [k: string]: string;
+}
+```
+
+## API
+
+All APIs can be found in the
+[deno doc](https://doc.deno.land/https/deno.land/x/authorization_parser/mod.ts).
+
+## License
+
+Copyright © 2023-present [httpland](https://github.com/httpland).
+
+Released under the [MIT](./LICENSE) license