ContainerImage.Pinniped/internal/oidc/auth/auth_handler_test.go

// Copyright 2020 the Pinniped contributors. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0

package auth

import (
	"fmt"
	"html"
	"mime"
	"net/http"
	"net/http/httptest"
	"net/url"
	"strings"
	"testing"

	"github.com/gorilla/securecookie"
	"github.com/ory/fosite"
	"github.com/ory/fosite/storage"
	"github.com/stretchr/testify/require"

	"go.pinniped.dev/internal/here"
	"go.pinniped.dev/internal/oidc"
	"go.pinniped.dev/internal/oidc/csrftoken"
	"go.pinniped.dev/internal/oidc/provider"
	"go.pinniped.dev/internal/oidcclient/nonce"
	"go.pinniped.dev/internal/oidcclient/pkce"
)

func TestAuthorizationEndpoint(t *testing.T) {
	const (
		downstreamRedirectURI                  = "http://127.0.0.1/callback"
		downstreamRedirectURIWithDifferentPort = "http://127.0.0.1:42/callback"
	)

	var (
		fositeInvalidClientErrorBody = here.Doc(`
			{
				"error":             "invalid_client",
				"error_verbose":     "Client authentication failed (e.g., unknown client, no client authentication included, or unsupported authentication method)",
				"error_description": "Client authentication failed (e.g., unknown client, no client authentication included, or unsupported authentication method)\n\nThe requested OAuth 2.0 Client does not exist.",
				"error_hint":        "The requested OAuth 2.0 Client does not exist.",
				"status_code":       401
			 }
		`)

		fositeInvalidRedirectURIErrorBody = here.Doc(`
			{
				"error":             "invalid_request",
				"error_verbose":     "The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed",
				"error_description": "The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed\n\nThe \"redirect_uri\" parameter does not match any of the OAuth 2.0 Client's pre-registered redirect urls.",
				"error_hint":        "The \"redirect_uri\" parameter does not match any of the OAuth 2.0 Client's pre-registered redirect urls.",
				"status_code":       400
			}
		`)

		fositePromptHasNoneAndOtherValueErrorQuery = map[string]string{
			"error":             "invalid_request",
			"error_description": "The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed\n\nParameter \"prompt\" was set to \"none\", but contains other values as well which is not allowed.",
			"error_hint":        "Parameter \"prompt\" was set to \"none\", but contains other values as well which is not allowed.",
			"state":             "some-state-value",
		}

		fositeMissingCodeChallengeErrorQuery = map[string]string{
			"error":             "invalid_request",
			"error_description": "The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed\n\nThis client must include a code_challenge when performing the authorize code flow, but it is missing.",
			"error_hint":        "This client must include a code_challenge when performing the authorize code flow, but it is missing.",
			"state":             "some-state-value",
		}

		fositeMissingCodeChallengeMethodErrorQuery = map[string]string{
			"error":             "invalid_request",
			"error_description": "The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed\n\nClients must use code_challenge_method=S256, plain is not allowed.",
			"error_hint":        "Clients must use code_challenge_method=S256, plain is not allowed.",
			"state":             "some-state-value",
		}

		fositeInvalidCodeChallengeErrorQuery = map[string]string{
			"error":             "invalid_request",
			"error_description": "The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed\n\nThe code_challenge_method is not supported, use S256 instead.",
			"error_hint":        "The code_challenge_method is not supported, use S256 instead.",
			"state":             "some-state-value",
		}

		fositeUnsupportedResponseTypeErrorQuery = map[string]string{
			"error":             "unsupported_response_type",
			"error_description": "The authorization server does not support obtaining a token using this method\n\nThe client is not allowed to request response_type \"unsupported\".",
			"error_hint":        `The client is not allowed to request response_type "unsupported".`,
			"state":             "some-state-value",
		}

		fositeInvalidScopeErrorQuery = map[string]string{
			"error":             "invalid_scope",
			"error_description": "The requested scope is invalid, unknown, or malformed\n\nThe OAuth 2.0 Client is not allowed to request scope \"tuna\".",
			"error_hint":        `The OAuth 2.0 Client is not allowed to request scope "tuna".`,
			"state":             "some-state-value",
		}

		fositeInvalidStateErrorQuery = map[string]string{
			"error":             "invalid_state",
			"error_description": "The state is missing or does not have enough characters and is therefore considered too weak\n\nRequest parameter \"state\" must be at least be 8 characters long to ensure sufficient entropy.",
			"error_hint":        `Request parameter "state" must be at least be 8 characters long to ensure sufficient entropy.`,
			"state":             "short",
		}

		fositeMissingResponseTypeErrorQuery = map[string]string{
			"error":             "unsupported_response_type",
			"error_description": "The authorization server does not support obtaining a token using this method\n\nThe request is missing the \"response_type\"\" parameter.",
			"error_hint":        `The request is missing the "response_type"" parameter.`,
			"state":             "some-state-value",
		}
	)

	upstreamAuthURL, err := url.Parse("https://some-upstream-idp:8443/auth")
	require.NoError(t, err)

	upstreamOIDCIdentityProvider := provider.UpstreamOIDCIdentityProvider{
		Name:             "some-idp",
		ClientID:         "some-client-id",
		AuthorizationURL: *upstreamAuthURL,
		Scopes:           []string{"scope1", "scope2"},
	}

	issuer := "https://my-issuer.com/some-path"

	// Configure fosite the same way that the production code would, except use in-memory storage.
	oauthStore := &storage.MemoryStore{
		Clients:        map[string]fosite.Client{oidc.PinnipedCLIOIDCClient().ID: oidc.PinnipedCLIOIDCClient()},
		AuthorizeCodes: map[string]storage.StoreAuthorizeCode{},
		PKCES:          map[string]fosite.Requester{},
		IDSessions:     map[string]fosite.Requester{},
	}
	hmacSecret := []byte("some secret - must have at least 32 bytes")
	require.GreaterOrEqual(t, len(hmacSecret), 32, "fosite requires that hmac secrets have at least 32 bytes")
	oauthHelper := oidc.FositeOauth2Helper(oauthStore, hmacSecret)

	happyCSRF := "test-csrf"
	happyPKCE := "test-pkce"
	happyNonce := "test-nonce"
	happyCSRFGenerator := func() (csrftoken.CSRFToken, error) { return csrftoken.CSRFToken(happyCSRF), nil }
	happyPKCEGenerator := func() (pkce.Code, error) { return pkce.Code(happyPKCE), nil }
	happyNonceGenerator := func() (nonce.Nonce, error) { return nonce.Nonce(happyNonce), nil }

	// This is the PKCE challenge which is calculated as base64(sha256("test-pkce")). For example:
	// $ echo -n test-pkce | shasum -a 256 | cut -d" " -f1 | xxd -r -p | base64 | cut -d"=" -f1
	expectedUpstreamCodeChallenge := "VVaezYqum7reIhoavCHD1n2d-piN3r_mywoYj7fCR7g"

	var encoderHashKey = []byte("fake-hash-secret")
	var happyEncoder = securecookie.New(encoderHashKey, nil) // note that nil block key argument turns off encryption
	happyEncoder.SetSerializer(securecookie.JSONEncoder{})

	encodeQuery := func(query map[string]string) string {
		values := url.Values{}
		for k, v := range query {
			values[k] = []string{v}
		}
		return values.Encode()
	}

	pathWithQuery := func(path string, query map[string]string) string {
		pathToReturn := fmt.Sprintf("%s?%s", path, encodeQuery(query))
		require.NotRegexp(t, "^http", pathToReturn, "pathWithQuery helper was used to create a URL")
		return pathToReturn
	}

	urlWithQuery := func(baseURL string, query map[string]string) string {
		urlToReturn := fmt.Sprintf("%s?%s", baseURL, encodeQuery(query))
		_, err := url.Parse(urlToReturn)
		require.NoError(t, err, "urlWithQuery helper was used to create an illegal URL")
		return urlToReturn
	}

	happyGetRequestQueryMap := map[string]string{
		"response_type":         "code",
		"scope":                 "openid profile email",
		"client_id":             "pinniped-cli",
		"state":                 "some-state-value",
		"nonce":                 "some-nonce-value",
		"code_challenge":        "some-challenge",
		"code_challenge_method": "S256",
		"redirect_uri":          downstreamRedirectURI,
	}

	happyGetRequestPath := pathWithQuery("/some/path", happyGetRequestQueryMap)

	modifiedHappyGetRequestQueryMap := func(queryOverrides map[string]string) map[string]string {
		copyOfHappyGetRequestQueryMap := map[string]string{}
		for k, v := range happyGetRequestQueryMap {
			copyOfHappyGetRequestQueryMap[k] = v
		}
		for k, v := range queryOverrides {
			_, hasKey := copyOfHappyGetRequestQueryMap[k]
			if v == "" && hasKey {
				delete(copyOfHappyGetRequestQueryMap, k)
			} else {
				copyOfHappyGetRequestQueryMap[k] = v
			}
		}
		return copyOfHappyGetRequestQueryMap
	}

	modifiedHappyGetRequestPath := func(queryOverrides map[string]string) string {
		return pathWithQuery("/some/path", modifiedHappyGetRequestQueryMap(queryOverrides))
	}

	expectedUpstreamStateParam := func(queryOverrides map[string]string) string {
		encoded, err := happyEncoder.Encode("s",
			expectedUpstreamStateParamFormat{
				P: encodeQuery(modifiedHappyGetRequestQueryMap(queryOverrides)),
				N: happyNonce,
				C: happyCSRF,
				K: happyPKCE,
				V: "1",
			},
		)
		require.NoError(t, err)
		return encoded
	}

	expectedRedirectLocation := func(expectedUpstreamState string) string {
		return urlWithQuery(upstreamAuthURL.String(), map[string]string{
			"response_type":         "code",
			"access_type":           "offline",
			"scope":                 "scope1 scope2",
			"client_id":             "some-client-id",
			"state":                 expectedUpstreamState,
			"nonce":                 happyNonce,
			"code_challenge":        expectedUpstreamCodeChallenge,
			"code_challenge_method": "S256",
			"redirect_uri":          issuer + "/callback/some-idp",
		})
	}

	happyCSRFSetCookieHeaderValue := fmt.Sprintf("__Host-pinniped-csrf=%s; HttpOnly; Secure; SameSite=Strict", happyCSRF)

	type testCase struct {
		name string

		issuer        string
		idpListGetter provider.DynamicUpstreamIDPProvider
		generateCSRF  func() (csrftoken.CSRFToken, error)
		generatePKCE  func() (pkce.Code, error)
		generateNonce func() (nonce.Nonce, error)
		encoder       securecookie.Codec
		method        string
		path          string
		contentType   string
		body          string

		wantStatus           int
		wantContentType      string
		wantBodyString       string
		wantBodyJSON         string
		wantLocationHeader   string
		wantCSRFCookieHeader string

		wantUpstreamStateParamInLocationHeader bool
	}
	tests := []testCase{
		{
			name:            "happy path using GET",
			issuer:          issuer,
			idpListGetter:   newIDPListGetter(upstreamOIDCIdentityProvider),
			generateCSRF:    happyCSRFGenerator,
			generatePKCE:    happyPKCEGenerator,
			generateNonce:   happyNonceGenerator,
			encoder:         happyEncoder,
			method:          http.MethodGet,
			path:            happyGetRequestPath,
			wantStatus:      http.StatusFound,
			wantContentType: "text/html; charset=utf-8",
			wantBodyString: fmt.Sprintf(`<a href="%s">Found</a>.%s`,
				html.EscapeString(expectedRedirectLocation(expectedUpstreamStateParam(nil))),
				"\n\n",
			),
			wantCSRFCookieHeader:                   happyCSRFSetCookieHeaderValue,
			wantLocationHeader:                     expectedRedirectLocation(expectedUpstreamStateParam(nil)),
			wantUpstreamStateParamInLocationHeader: true,
		},
		{
			name:                                   "happy path using POST",
			issuer:                                 issuer,
			idpListGetter:                          newIDPListGetter(upstreamOIDCIdentityProvider),
			generateCSRF:                           happyCSRFGenerator,
			generatePKCE:                           happyPKCEGenerator,
			generateNonce:                          happyNonceGenerator,
			encoder:                                happyEncoder,
			method:                                 http.MethodPost,
			path:                                   "/some/path",
			contentType:                            "application/x-www-form-urlencoded",
			body:                                   encodeQuery(happyGetRequestQueryMap),
			wantStatus:                             http.StatusFound,
			wantContentType:                        "",
			wantBodyString:                         "",
			wantCSRFCookieHeader:                   happyCSRFSetCookieHeaderValue,
			wantLocationHeader:                     expectedRedirectLocation(expectedUpstreamStateParam(nil)),
			wantUpstreamStateParamInLocationHeader: true,
		},
		{
			name:          "happy path when downstream redirect uri matches what is configured for client except for the port number",
			issuer:        issuer,
			idpListGetter: newIDPListGetter(upstreamOIDCIdentityProvider),
			generateCSRF:  happyCSRFGenerator,
			generatePKCE:  happyPKCEGenerator,
			generateNonce: happyNonceGenerator,
			encoder:       happyEncoder,
			method:        http.MethodGet,
			path: modifiedHappyGetRequestPath(map[string]string{
				"redirect_uri": downstreamRedirectURIWithDifferentPort, // not the same port number that is registered for the client
			}),
			wantStatus:      http.StatusFound,
			wantContentType: "text/html; charset=utf-8",
			wantBodyString: fmt.Sprintf(`<a href="%s">Found</a>.%s`,
				html.EscapeString(expectedRedirectLocation(expectedUpstreamStateParam(map[string]string{
					"redirect_uri": downstreamRedirectURIWithDifferentPort, // not the same port number that is registered for the client
				}))),
				"\n\n",
			),
			wantCSRFCookieHeader: happyCSRFSetCookieHeaderValue,
			wantLocationHeader: expectedRedirectLocation(expectedUpstreamStateParam(map[string]string{
				"redirect_uri": downstreamRedirectURIWithDifferentPort, // not the same port number that is registered for the client
			})),
			wantUpstreamStateParamInLocationHeader: true,
		},
		{
			name:          "downstream redirect uri does not match what is configured for client",
			issuer:        issuer,
			idpListGetter: newIDPListGetter(upstreamOIDCIdentityProvider),
			generateCSRF:  happyCSRFGenerator,
			generatePKCE:  happyPKCEGenerator,
			generateNonce: happyNonceGenerator,
			encoder:       happyEncoder,
			method:        http.MethodGet,
			path: modifiedHappyGetRequestPath(map[string]string{
				"redirect_uri": "http://127.0.0.1/does-not-match-what-is-configured-for-pinniped-cli-client",
			}),
			wantStatus:      http.StatusBadRequest,
			wantContentType: "application/json; charset=utf-8",
			wantBodyJSON:    fositeInvalidRedirectURIErrorBody,
		},
		{
			name:            "downstream client does not exist",
			issuer:          issuer,
			idpListGetter:   newIDPListGetter(upstreamOIDCIdentityProvider),
			generateCSRF:    happyCSRFGenerator,
			generatePKCE:    happyPKCEGenerator,
			generateNonce:   happyNonceGenerator,
			encoder:         happyEncoder,
			method:          http.MethodGet,
			path:            modifiedHappyGetRequestPath(map[string]string{"client_id": "invalid-client"}),
			wantStatus:      http.StatusUnauthorized,
			wantContentType: "application/json; charset=utf-8",
			wantBodyJSON:    fositeInvalidClientErrorBody,
		},
		{
			name:               "response type is unsupported",
			issuer:             issuer,
			idpListGetter:      newIDPListGetter(upstreamOIDCIdentityProvider),
			generateCSRF:       happyCSRFGenerator,
			generatePKCE:       happyPKCEGenerator,
			generateNonce:      happyNonceGenerator,
			encoder:            happyEncoder,
			method:             http.MethodGet,
			path:               modifiedHappyGetRequestPath(map[string]string{"response_type": "unsupported"}),
			wantStatus:         http.StatusFound,
			wantContentType:    "application/json; charset=utf-8",
			wantLocationHeader: urlWithQuery(downstreamRedirectURI, fositeUnsupportedResponseTypeErrorQuery),
			wantBodyString:     "",
		},
		{
			name:               "downstream scopes do not match what is configured for client",
			issuer:             issuer,
			idpListGetter:      newIDPListGetter(upstreamOIDCIdentityProvider),
			generateCSRF:       happyCSRFGenerator,
			generatePKCE:       happyPKCEGenerator,
			generateNonce:      happyNonceGenerator,
			encoder:            happyEncoder,
			method:             http.MethodGet,
			path:               modifiedHappyGetRequestPath(map[string]string{"scope": "openid profile email tuna"}),
			wantStatus:         http.StatusFound,
			wantContentType:    "application/json; charset=utf-8",
			wantLocationHeader: urlWithQuery(downstreamRedirectURI, fositeInvalidScopeErrorQuery),
			wantBodyString:     "",
		},
		{
			name:               "missing response type in request",
			issuer:             issuer,
			idpListGetter:      newIDPListGetter(upstreamOIDCIdentityProvider),
			generateCSRF:       happyCSRFGenerator,
			generatePKCE:       happyPKCEGenerator,
			generateNonce:      happyNonceGenerator,
			encoder:            happyEncoder,
			method:             http.MethodGet,
			path:               modifiedHappyGetRequestPath(map[string]string{"response_type": ""}),
			wantStatus:         http.StatusFound,
			wantContentType:    "application/json; charset=utf-8",
			wantLocationHeader: urlWithQuery(downstreamRedirectURI, fositeMissingResponseTypeErrorQuery),
			wantBodyString:     "",
		},
		{
			name:            "missing client id in request",
			issuer:          issuer,
			idpListGetter:   newIDPListGetter(upstreamOIDCIdentityProvider),
			generateCSRF:    happyCSRFGenerator,
			generatePKCE:    happyPKCEGenerator,
			generateNonce:   happyNonceGenerator,
			encoder:         happyEncoder,
			method:          http.MethodGet,
			path:            modifiedHappyGetRequestPath(map[string]string{"client_id": ""}),
			wantStatus:      http.StatusUnauthorized,
			wantContentType: "application/json; charset=utf-8",
			wantBodyJSON:    fositeInvalidClientErrorBody,
		},
		{
			name:               "missing PKCE code_challenge in request", // See https://tools.ietf.org/html/rfc7636#section-4.4.1
			issuer:             issuer,
			idpListGetter:      newIDPListGetter(upstreamOIDCIdentityProvider),
			generateCSRF:       happyCSRFGenerator,
			generatePKCE:       happyPKCEGenerator,
			generateNonce:      happyNonceGenerator,
			encoder:            happyEncoder,
			method:             http.MethodGet,
			path:               modifiedHappyGetRequestPath(map[string]string{"code_challenge": ""}),
			wantStatus:         http.StatusFound,
			wantContentType:    "application/json; charset=utf-8",
			wantLocationHeader: urlWithQuery(downstreamRedirectURI, fositeMissingCodeChallengeErrorQuery),
			wantBodyString:     "",
		},
		{
			name:               "invalid value for PKCE code_challenge_method in request", // https://tools.ietf.org/html/rfc7636#section-4.3
			issuer:             issuer,
			idpListGetter:      newIDPListGetter(upstreamOIDCIdentityProvider),
			generateCSRF:       happyCSRFGenerator,
			generatePKCE:       happyPKCEGenerator,
			generateNonce:      happyNonceGenerator,
			encoder:            happyEncoder,
			method:             http.MethodGet,
			path:               modifiedHappyGetRequestPath(map[string]string{"code_challenge_method": "this-is-not-a-valid-pkce-alg"}),
			wantStatus:         http.StatusFound,
			wantContentType:    "application/json; charset=utf-8",
			wantLocationHeader: urlWithQuery(downstreamRedirectURI, fositeInvalidCodeChallengeErrorQuery),
			wantBodyString:     "",
		},
		{
			name:               "when PKCE code_challenge_method in request is `plain`", // https://tools.ietf.org/html/rfc7636#section-4.3
			issuer:             issuer,
			idpListGetter:      newIDPListGetter(upstreamOIDCIdentityProvider),
			generateCSRF:       happyCSRFGenerator,
			generatePKCE:       happyPKCEGenerator,
			generateNonce:      happyNonceGenerator,
			encoder:            happyEncoder,
			method:             http.MethodGet,
			path:               modifiedHappyGetRequestPath(map[string]string{"code_challenge_method": "plain"}),
			wantStatus:         http.StatusFound,
			wantContentType:    "application/json; charset=utf-8",
			wantLocationHeader: urlWithQuery(downstreamRedirectURI, fositeMissingCodeChallengeMethodErrorQuery),
			wantBodyString:     "",
		},
		{
			name:               "missing PKCE code_challenge_method in request", // See https://tools.ietf.org/html/rfc7636#section-4.4.1
			issuer:             issuer,
			idpListGetter:      newIDPListGetter(upstreamOIDCIdentityProvider),
			generateCSRF:       happyCSRFGenerator,
			generatePKCE:       happyPKCEGenerator,
			generateNonce:      happyNonceGenerator,
			encoder:            happyEncoder,
			method:             http.MethodGet,
			path:               modifiedHappyGetRequestPath(map[string]string{"code_challenge_method": ""}),
			wantStatus:         http.StatusFound,
			wantContentType:    "application/json; charset=utf-8",
			wantLocationHeader: urlWithQuery(downstreamRedirectURI, fositeMissingCodeChallengeMethodErrorQuery),
			wantBodyString:     "",
		},
		{
			// This is just one of the many OIDC validations run by fosite. This test is to ensure that we are running
			// through that part of the fosite library.
			name:               "prompt param is not allowed to have none and another legal value at the same time",
			issuer:             issuer,
			idpListGetter:      newIDPListGetter(upstreamOIDCIdentityProvider),
			generateCSRF:       happyCSRFGenerator,
			generatePKCE:       happyPKCEGenerator,
			generateNonce:      happyNonceGenerator,
			encoder:            happyEncoder,
			method:             http.MethodGet,
			path:               modifiedHappyGetRequestPath(map[string]string{"prompt": "none login"}),
			wantStatus:         http.StatusFound,
			wantContentType:    "application/json; charset=utf-8",
			wantLocationHeader: urlWithQuery(downstreamRedirectURI, fositePromptHasNoneAndOtherValueErrorQuery),
			wantBodyString:     "",
		},
		{
			name:          "OIDC validations are skipped when the openid scope was not requested",
			issuer:        issuer,
			idpListGetter: newIDPListGetter(upstreamOIDCIdentityProvider),
			generateCSRF:  happyCSRFGenerator,
			generatePKCE:  happyPKCEGenerator,
			generateNonce: happyNonceGenerator,
			encoder:       happyEncoder,
			method:        http.MethodGet,
			// The following prompt value is illegal when openid is requested, but note that openid is not requested.
			path:            modifiedHappyGetRequestPath(map[string]string{"prompt": "none login", "scope": "email"}),
			wantStatus:      http.StatusFound,
			wantContentType: "text/html; charset=utf-8",
			wantBodyString: fmt.Sprintf(`<a href="%s">Found</a>.%s`,
				html.EscapeString(expectedRedirectLocation(expectedUpstreamStateParam(map[string]string{"prompt": "none login", "scope": "email"}))),
				"\n\n",
			),
			wantCSRFCookieHeader:                   happyCSRFSetCookieHeaderValue,
			wantLocationHeader:                     expectedRedirectLocation(expectedUpstreamStateParam(map[string]string{"prompt": "none login", "scope": "email"})),
			wantUpstreamStateParamInLocationHeader: true,
		},
		{
			name:               "state does not have enough entropy",
			issuer:             issuer,
			idpListGetter:      newIDPListGetter(upstreamOIDCIdentityProvider),
			generateCSRF:       happyCSRFGenerator,
			generatePKCE:       happyPKCEGenerator,
			generateNonce:      happyNonceGenerator,
			encoder:            happyEncoder,
			method:             http.MethodGet,
			path:               modifiedHappyGetRequestPath(map[string]string{"state": "short"}),
			wantStatus:         http.StatusFound,
			wantContentType:    "application/json; charset=utf-8",
			wantLocationHeader: urlWithQuery(downstreamRedirectURI, fositeInvalidStateErrorQuery),
			wantBodyString:     "",
		},
		{
			name:            "error while encoding upstream state param",
			issuer:          issuer,
			idpListGetter:   newIDPListGetter(upstreamOIDCIdentityProvider),
			generateCSRF:    happyCSRFGenerator,
			generatePKCE:    happyPKCEGenerator,
			generateNonce:   happyNonceGenerator,
			encoder:         &errorReturningEncoder{},
			method:          http.MethodGet,
			path:            happyGetRequestPath,
			wantStatus:      http.StatusInternalServerError,
			wantContentType: "text/plain; charset=utf-8",
			wantBodyString:  "Internal Server Error: error encoding upstream state param\n",
		},
		{
			name:            "error while generating CSRF token",
			issuer:          issuer,
			idpListGetter:   newIDPListGetter(upstreamOIDCIdentityProvider),
			generateCSRF:    func() (csrftoken.CSRFToken, error) { return "", fmt.Errorf("some csrf generator error") },
			generatePKCE:    happyPKCEGenerator,
			generateNonce:   happyNonceGenerator,
			encoder:         happyEncoder,
			method:          http.MethodGet,
			path:            happyGetRequestPath,
			wantStatus:      http.StatusInternalServerError,
			wantContentType: "text/plain; charset=utf-8",
			wantBodyString:  "Internal Server Error: error generating CSRF token\n",
		},
		{
			name:            "error while generating nonce",
			issuer:          issuer,
			idpListGetter:   newIDPListGetter(upstreamOIDCIdentityProvider),
			generateCSRF:    happyCSRFGenerator,
			generatePKCE:    happyPKCEGenerator,
			generateNonce:   func() (nonce.Nonce, error) { return "", fmt.Errorf("some nonce generator error") },
			encoder:         happyEncoder,
			method:          http.MethodGet,
			path:            happyGetRequestPath,
			wantStatus:      http.StatusInternalServerError,
			wantContentType: "text/plain; charset=utf-8",
			wantBodyString:  "Internal Server Error: error generating nonce param\n",
		},
		{
			name:            "error while generating PKCE",
			issuer:          issuer,
			idpListGetter:   newIDPListGetter(upstreamOIDCIdentityProvider),
			generateCSRF:    happyCSRFGenerator,
			generatePKCE:    func() (pkce.Code, error) { return "", fmt.Errorf("some PKCE generator error") },
			generateNonce:   happyNonceGenerator,
			encoder:         happyEncoder,
			method:          http.MethodGet,
			path:            happyGetRequestPath,
			wantStatus:      http.StatusInternalServerError,
			wantContentType: "text/plain; charset=utf-8",
			wantBodyString:  "Internal Server Error: error generating PKCE param\n",
		},
		{
			name:            "no upstream providers are configured",
			issuer:          issuer,
			idpListGetter:   newIDPListGetter(), // empty
			method:          http.MethodGet,
			path:            happyGetRequestPath,
			wantStatus:      http.StatusUnprocessableEntity,
			wantContentType: "text/plain; charset=utf-8",
			wantBodyString:  "Unprocessable Entity: No upstream providers are configured\n",
		},
		{
			name:            "too many upstream providers are configured",
			issuer:          issuer,
			idpListGetter:   newIDPListGetter(upstreamOIDCIdentityProvider, upstreamOIDCIdentityProvider), // more than one not allowed
			method:          http.MethodGet,
			path:            happyGetRequestPath,
			wantStatus:      http.StatusUnprocessableEntity,
			wantContentType: "text/plain; charset=utf-8",
			wantBodyString:  "Unprocessable Entity: Too many upstream providers are configured (support for multiple upstreams is not yet implemented)\n",
		},
		{
			name:            "PUT is a bad method",
			issuer:          issuer,
			idpListGetter:   newIDPListGetter(upstreamOIDCIdentityProvider),
			method:          http.MethodPut,
			path:            "/some/path",
			wantStatus:      http.StatusMethodNotAllowed,
			wantContentType: "text/plain; charset=utf-8",
			wantBodyString:  "Method Not Allowed: PUT (try GET or POST)\n",
		},
		{
			name:            "PATCH is a bad method",
			issuer:          issuer,
			idpListGetter:   newIDPListGetter(upstreamOIDCIdentityProvider),
			method:          http.MethodPatch,
			path:            "/some/path",
			wantStatus:      http.StatusMethodNotAllowed,
			wantContentType: "text/plain; charset=utf-8",
			wantBodyString:  "Method Not Allowed: PATCH (try GET or POST)\n",
		},
		{
			name:            "DELETE is a bad method",
			issuer:          issuer,
			idpListGetter:   newIDPListGetter(upstreamOIDCIdentityProvider),
			method:          http.MethodDelete,
			path:            "/some/path",
			wantStatus:      http.StatusMethodNotAllowed,
			wantContentType: "text/plain; charset=utf-8",
			wantBodyString:  "Method Not Allowed: DELETE (try GET or POST)\n",
		},
	}

	runOneTestCase := func(t *testing.T, test testCase, subject http.Handler) {
		req := httptest.NewRequest(test.method, test.path, strings.NewReader(test.body))
		req.Header.Set("Content-Type", test.contentType)
		rsp := httptest.NewRecorder()
		subject.ServeHTTP(rsp, req)

		require.Equal(t, test.wantStatus, rsp.Code)
		requireEqualContentType(t, rsp.Header().Get("Content-Type"), test.wantContentType)

		if test.wantLocationHeader != "" {
			actualLocation := rsp.Header().Get("Location")
			if test.wantUpstreamStateParamInLocationHeader {
				requireEqualDecodedStateParams(t, actualLocation, test.wantLocationHeader, test.encoder)
			}
			requireEqualURLs(t, actualLocation, test.wantLocationHeader)
		} else {
			require.Empty(t, rsp.Header().Values("Location"))
		}

		if test.wantBodyJSON != "" {
			require.JSONEq(t, test.wantBodyJSON, rsp.Body.String())
		} else {
			require.Equal(t, test.wantBodyString, rsp.Body.String())
		}

		if test.wantCSRFCookieHeader != "" {
			require.Len(t, rsp.Header().Values("Set-Cookie"), 1)
			actualCookie := rsp.Header().Get("Set-Cookie")
			require.Equal(t, actualCookie, test.wantCSRFCookieHeader)
		} else {
			require.Empty(t, rsp.Header().Values("Set-Cookie"))
		}
	}

	for _, test := range tests {
		test := test
		t.Run(test.name, func(t *testing.T) {
			subject := NewHandler(test.issuer, test.idpListGetter, oauthHelper, test.generateCSRF, test.generatePKCE, test.generateNonce, test.encoder)
			runOneTestCase(t, test, subject)
		})
	}

	t.Run("allows upstream provider configuration to change between requests", func(t *testing.T) {
		test := tests[0]
		require.Equal(t, "happy path using GET", test.name) // re-use the happy path test case

		subject := NewHandler(test.issuer, test.idpListGetter, oauthHelper, test.generateCSRF, test.generatePKCE, test.generateNonce, test.encoder)

		runOneTestCase(t, test, subject)

		// Call the setter to change the upstream IDP settings.
		newProviderSettings := provider.UpstreamOIDCIdentityProvider{
			Name:             "some-other-idp",
			ClientID:         "some-other-client-id",
			AuthorizationURL: *upstreamAuthURL,
			Scopes:           []string{"other-scope1", "other-scope2"},
		}
		test.idpListGetter.SetIDPList([]provider.UpstreamOIDCIdentityProvider{newProviderSettings})

		// Update the expectations of the test case to match the new upstream IDP settings.
		test.wantLocationHeader = urlWithQuery(upstreamAuthURL.String(),
			map[string]string{
				"response_type":         "code",
				"access_type":           "offline",
				"scope":                 "other-scope1 other-scope2",
				"client_id":             "some-other-client-id",
				"state":                 expectedUpstreamStateParam(nil),
				"nonce":                 happyNonce,
				"code_challenge":        expectedUpstreamCodeChallenge,
				"code_challenge_method": "S256",
				"redirect_uri":          issuer + "/callback/some-other-idp",
			},
		)
		test.wantBodyString = fmt.Sprintf(`<a href="%s">Found</a>.%s`,
			html.EscapeString(test.wantLocationHeader),
			"\n\n",
		)

		// Run again on the same instance of the subject with the modified upstream IDP settings and the
		// modified expectations. This should ensure that the implementation is using the in-memory cache
		// of upstream IDP settings appropriately in terms of always getting the values from the cache
		// on every request.
		runOneTestCase(t, test, subject)
	})
}

// Declare a separate type from the production code to ensure that the state param's contents was serialized
// in the format that we expect, with the json keys that we expect, etc. This also ensure that the order of
// the serialized fields is the same, which doesn't really matter expect that we can make simpler equality
// assertions about the redirect URL in this test.
type expectedUpstreamStateParamFormat struct {
	P string `json:"p"`
	N string `json:"n"`
	C string `json:"c"`
	K string `json:"k"`
	V string `json:"v"`
}

type errorReturningEncoder struct {
	securecookie.Codec
}

func (*errorReturningEncoder) Encode(_ string, _ interface{}) (string, error) {
	return "", fmt.Errorf("some encoding error")
}

func requireEqualContentType(t *testing.T, actual string, expected string) {
	t.Helper()

	if expected == "" {
		require.Empty(t, actual)
		return
	}

	actualContentType, actualContentTypeParams, err := mime.ParseMediaType(expected)
	require.NoError(t, err)
	expectedContentType, expectedContentTypeParams, err := mime.ParseMediaType(expected)
	require.NoError(t, err)
	require.Equal(t, actualContentType, expectedContentType)
	require.Equal(t, actualContentTypeParams, expectedContentTypeParams)
}

func requireEqualDecodedStateParams(t *testing.T, actualURL string, expectedURL string, stateParamDecoder securecookie.Codec) {
	t.Helper()
	actualLocationURL, err := url.Parse(actualURL)
	require.NoError(t, err)
	expectedLocationURL, err := url.Parse(expectedURL)
	require.NoError(t, err)

	expectedQueryStateParam := expectedLocationURL.Query().Get("state")
	require.NotEmpty(t, expectedQueryStateParam)
	var expectedDecodedStateParam expectedUpstreamStateParamFormat
	err = stateParamDecoder.Decode("s", expectedQueryStateParam, &expectedDecodedStateParam)
	require.NoError(t, err)

	actualQueryStateParam := actualLocationURL.Query().Get("state")
	require.NotEmpty(t, actualQueryStateParam)
	var actualDecodedStateParam expectedUpstreamStateParamFormat
	err = stateParamDecoder.Decode("s", actualQueryStateParam, &actualDecodedStateParam)
	require.NoError(t, err)

	require.Equal(t, expectedDecodedStateParam, actualDecodedStateParam)
}

func requireEqualURLs(t *testing.T, actualURL string, expectedURL string) {
	t.Helper()
	actualLocationURL, err := url.Parse(actualURL)
	require.NoError(t, err)
	expectedLocationURL, err := url.Parse(expectedURL)
	require.NoError(t, err)
	require.Equal(t, expectedLocationURL.Scheme, actualLocationURL.Scheme)
	require.Equal(t, expectedLocationURL.User, actualLocationURL.User)
	require.Equal(t, expectedLocationURL.Host, actualLocationURL.Host)
	require.Equal(t, expectedLocationURL.Path, actualLocationURL.Path)
	require.Equal(t, expectedLocationURL.Query(), actualLocationURL.Query())
}

func newIDPListGetter(upstreamOIDCIdentityProviders ...provider.UpstreamOIDCIdentityProvider) provider.DynamicUpstreamIDPProvider {
	idpProvider := provider.NewDynamicUpstreamIDPProvider()
	idpProvider.SetIDPList(upstreamOIDCIdentityProviders)
	return idpProvider
}