structured config #3: support for proxy options

[tuunit]

Description

Warning

This is a PR stacked on top of:

• introduce mapstructure decoder for yaml parsing #2628
• legacy file structure refactoring and cookie support #2629

Actual stacked changes can be viewed here:
https://github.com/tuunit/oauth2-proxy/pull/8/files

Adding support for proxy behaviour options:

	AllowQuerySemicolons  bool     `json:"allowQuerySemicolons,omitempty"`
	ForceHTTPS            bool     `json:"forceHttps,omitempty"`
	SkipAuthRegex         []string `json:"skipAuthRegex,omitempty"`
	SkipAuthRoutes        []string `json:"skipAuthRoutes,omitempty"`
	SkipAuthPreflight     bool     `json:"skipAuthPreflight,omitempty"`
	SSLInsecureSkipVerify bool     `json:"sslInsecureSkipVerify,omitempty"`
	TrustedIPs            []string `json:"trustedIPs,omitempty"`

	// authentication
	AuthenticatedEmailsFile string   `json:"authenticatedEmailsFile,omitempty"`
	EmailDomains            []string `json:"emailDomains,omitempty"`
	WhitelistDomains        []string `json:"whitelistDomains,omitempty"`
	HtpasswdFile            string   `json:"htpasswdFile,omitempty"`
	HtpasswdUserGroups      []string `json:"htpasswdUserGroups,omitempty"`
	SkipJwtBearerTokens     bool     `json:"skipJwtBearerTokens,omitempty"`
	ExtraJwtIssuers         []string `json:"extraJwtIssuers,omitempty"`

	// routing
	APIRoutes           []string `json:"apiRoutes,omitempty"`
	ReverseProxy        bool     `json:"reverseProxy,omitempty"`
	ProxyPrefix         string   `json:"proxyPrefix,omitempty"`
	RedirectURL         string   `json:"redirectUrl,omitempty"`
	RelativeRedirectURL bool     `json:"relativeRedirectUrl,omitempty"`
	RealClientIPHeader  string   `json:"realClientIPHeader,omitempty"`
	SkipProviderButton  bool     `json:"skipProviderButton,omitempty"`
	EncodeState         bool     `json:"encodeState,omitempty"`

	// Force oauth2-proxy error responses to be JSON
	ForceJSONErrors bool `json:"forceJsonErrors,omitempty"`

	// This is used for backwards compatibility
	LegacyPreferEmailToUser bool   `json:"legacyPreferEmailToUser,omitempty"`
	LegacySignatureKey      string `json:"legacySignatureKey,omitempty"`

How Has This Been Tested?

1. Test cases have been extend / adapted.
2. Starting the application with toml config file
3. Using the conversion function from toml to yaml
4. Starting the application with yaml config file

Checklist:

• My change requires a change to the documentation or CHANGELOG.
• I have updated the documentation/CHANGELOG accordingly.
• I have created a feature (non-master) branch for my PR.
• I have written tests for my code changes.