private string Html(GitHubAppManifest app) =>
$@"
<!DOCTYPE html>
<html lang=""en-US"">
<head>
<meta charset=""utf-8"">
<title>GitHub Provider Setup</title>
<style>
body {{ font-family: Helvetica, Arial, sans-serif; font-size: 14px; line-height: 1.5; color: #24292e; margin: 0; }}
.intro {{ display: flex; padding-bottom: 8px; padding-top: 40px; margin-bottom: 16px; border-bottom: 1px solid #e1e4e8; flex-flow: row wrap; }}
form, h1, button, .intro, .note {{ width: 474px; }}
h1 {{ font-size: 24px; font-weight: 400; flex: 1 1 auto; margin: 0; padding: 0; }}
.note, h1 {{ display: inline-block; }}
.note {{ min-height: 17px; margin: 4px 0 18px; font-size: 12px; color: #586069; }}
.intro, form {{ margin: 0 auto; }}
ul {{ list-style: none; padding: 2em 0 0; margin: 0; }}
a {{ color: #0366d6; text-decoration: none; }}
button {{ color: #fff; background-color: #28a745; background-image: linear-gradient(-180deg, #34d058, #28a745 90%); padding: 6px 12px; font-size: 14px; font-weight: 600; line-height: 20px; white-space: nowrap; vertical-align: middle; cursor: pointer; user-select: none; background-repeat: repeat-x; background-position: -1px -1px; background-size: 110% 110%; border: 1px solid rgba(27, 31, 35, .2); border-radius: .25em; -webkit-appearance: none; }}
header {{ background-color: #24292e; height: 53px; }}
</style>
</head>
<body>
<header></header>
<div class=""intro"">
<h1>GitHub Provider Setup</h1>
</div>
<form id=""manifest_form"" action=""https://github.com/apps/{app.Slug}/installations/new/permissions"">
<ul>
<input type=""hidden"" name=""target_id"" value=""{app.Owner.Id}"">
<li class=""button"">
<button type=""submit"">Install GitHub App on {app.Owner.Login}</button>
</li>
<li>
<p class=""note"">To install the app, you must be an organization owner or have <a href=""https://help.github.com/en/github/setting-up-and-managing-organizations-and-teams/permission-levels-for-an-organization#github-app-managers"">GitHub App manager</a> permissions.</p>
</li>
</ul>
</form>
</body>
</html>
";
private GitHubJwtFactory JwtTokenGenerator(GitHubAppManifest app) => new GitHubJwtFactory(
