diff --git a/clientapi/routing/register.go b/clientapi/routing/register.go
index feea3b049..2ac4f3c6a 100644
--- a/clientapi/routing/register.go
+++ b/clientapi/routing/register.go
@@ -19,7 +19,6 @@ import (
 	"context"
 	"crypto/hmac"
 	"crypto/sha1"
-	"crypto/tls"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -40,6 +39,7 @@ import (
 	"github.com/matrix-org/dendrite/clientapi/auth/authtypes"
 	"github.com/matrix-org/dendrite/clientapi/httputil"
 	"github.com/matrix-org/dendrite/clientapi/jsonerror"
+	"github.com/matrix-org/dendrite/clientapi/threepid"
 	"github.com/matrix-org/dendrite/clientapi/userutil"
 	userapi "github.com/matrix-org/dendrite/userapi/api"
 	"github.com/matrix-org/dendrite/userapi/storage/accounts"
@@ -161,33 +161,10 @@ type authDict struct {
 	// Recaptcha
 	Response string `json:"response"`
 	// m.login.email.identity and m.login.msisdn
-	ThreePidCreds *threepidCreds `json:"threepidCreds"`
+	ThreePidCreds *threepid.Credentials `json:"threepidCreds"`
 	// TODO: Lots of custom keys depending on the type
 }
 
-type threepidCreds struct {
-	Sid           string `json:"sid"`
-	ClientSecret  string `json:"client_secret"`
-	IdServer      string `json:"id_server"`
-	IdAccessToken string `json:"id_access_token"`
-}
-
-func (c *threepidCreds) validate() *jsonerror.MatrixError {
-	if c.Sid == "" {
-		return jsonerror.BadJSON("sid field in threepidCreds is required")
-	}
-	if c.ClientSecret == "" {
-		return jsonerror.BadJSON("client_secret in threepidCreds is required")
-	}
-	if c.IdServer == "" {
-		return jsonerror.BadJSON("id_server in threepidCreds is required")
-	}
-	if c.IdAccessToken == "" {
-		return jsonerror.BadJSON("id_access_token in threepidCreds is required")
-	}
-	return nil
-}
-
 // http://matrix.org/speculator/spec/HEAD/client_server/unstable.html#user-interactive-authentication-api
 type userInteractiveResponse struct {
 	Flows     []authtypes.Flow       `json:"flows"`
@@ -352,15 +329,19 @@ func validateRecaptcha(
 
 func validateEmailIdentity(
 	ctx context.Context,
-	cred *threepidCreds,
+	cred *threepid.Credentials,
+	cfg *config.ClientAPI,
 ) *util.JSONResponse {
+	if err := isTrusted(cred.IDServer, cfg); err != nil {
+		return &util.JSONResponse{
+			Code: http.StatusForbidden,
+			JSON: jsonerror.NotTrusted(cred.IDServer),
+		}
+	}
+	util.GetLogger(ctx).Infof("conecting to identity server: %s", cred.IDServer)
 	url := fmt.Sprintf(
 		"https://%s/_matrix/identity/api/v1/3pid/getValidated3pid",
-		cred.IdServer)
-	tr := &http.Transport{
-		TLSClientConfig: &tls.Config{InsecureSkipVerify: true},
-	}
-	client := &http.Client{Transport: tr}
+		cred.IDServer)
 	req, err := http.NewRequestWithContext(ctx, "POST", url, nil)
 	if err != nil {
 		return &util.JSONResponse{
@@ -369,11 +350,11 @@ func validateEmailIdentity(
 		}
 	}
 	q := req.URL.Query()
-	q.Add("client_secret", cred.ClientSecret)
-	q.Add("sid", cred.Sid)
+	q.Add("client_secret", cred.Secret)
+	q.Add("sid", cred.SID)
 	req.URL.RawQuery = q.Encode()
 	req.Header.Add("Authorization", "Bearer swordfish")
-	resp, err := client.Do(req)
+	resp, err := cfg.Derived.HttpClient.Do(req)
 	if err != nil {
 		util.GetLogger(ctx).WithError(err).Error("failed conecting to identity server")
 		return &util.JSONResponse{
@@ -403,6 +384,18 @@ func validateEmailIdentity(
 	}
 }
 
+// isTrusted checks if a given identity server is part of the list of trusted
+// identity servers in the configuration file.
+// Returns an error if the server isn't trusted.
+func isTrusted(idServer string, cfg *config.ClientAPI) error {
+	for _, server := range cfg.Matrix.TrustedIDServers {
+		if idServer == server {
+			return nil
+		}
+	}
+	return threepid.ErrNotTrusted
+}
+
 // UserIDIsWithinApplicationServiceNamespace checks to see if a given userID
 // falls within any of the namespaces of a given Application Service. If no
 // Application Service is given, it will check to see if it matches any
@@ -759,13 +752,13 @@ func handleRegistrationFlow(
 				JSON: jsonerror.BadJSON("threepidCreds not found in auth field"),
 			}
 		}
-		if err := r.Auth.ThreePidCreds.validate(); err != nil {
+		if err := r.Auth.ThreePidCreds.Validate(); err != nil {
 			return util.JSONResponse{
 				Code: http.StatusBadRequest,
 				JSON: err,
 			}
 		}
-		if err := validateEmailIdentity(req.Context(), r.Auth.ThreePidCreds); err != nil {
+		if err := validateEmailIdentity(req.Context(), r.Auth.ThreePidCreds, cfg); err != nil {
 			return *err
 		}
 		AddCompletedSessionStage(sessionID, authtypes.LoginTypeEmailIdentity)
diff --git a/clientapi/threepid/threepid.go b/clientapi/threepid/threepid.go
index 2f817ef42..49cb2ab29 100644
--- a/clientapi/threepid/threepid.go
+++ b/clientapi/threepid/threepid.go
@@ -15,15 +15,16 @@
 package threepid
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
 	"net/http"
 	"net/url"
-	"strconv"
 	"strings"
 
+	"github.com/matrix-org/dendrite/clientapi/jsonerror"
 	"github.com/matrix-org/dendrite/setup/config"
 )
 
@@ -48,6 +49,19 @@ type Credentials struct {
 	Secret   string `json:"client_secret"`
 }
 
+func (c *Credentials) Validate() *jsonerror.MatrixError {
+	if c.SID == "" {
+		return jsonerror.BadJSON("sid field in threepidCreds is required")
+	}
+	if c.Secret == "" {
+		return jsonerror.BadJSON("client_secret in threepidCreds is required")
+	}
+	if c.IDServer == "" {
+		return jsonerror.BadJSON("id_server in threepidCreds is required")
+	}
+	return nil
+}
+
 // CreateSession creates a session on an identity server.
 // Returns the session's ID.
 // Returns an error if there was a problem sending the request or decoding the
@@ -62,22 +76,23 @@ func CreateSession(
 	// Create a session on the ID server
 	postURL := fmt.Sprintf("https://%s/_matrix/identity/api/v1/validate/email/requestToken", req.IDServer)
 
-	data := url.Values{}
-	data.Add("client_secret", req.Secret)
-	data.Add("email", req.Email)
-	data.Add("send_attempt", strconv.Itoa(req.SendAttempt))
-
-	request, err := http.NewRequest(http.MethodPost, postURL, strings.NewReader(data.Encode()))
+	b := bytes.Buffer{}
+	enc := json.NewEncoder(&b)
+	err := enc.Encode(req)
 	if err != nil {
 		return "", err
 	}
-	request.Header.Add("Content-Type", "application/x-www-form-urlencoded")
-
-	client := http.Client{}
-	resp, err := client.Do(request.WithContext(ctx))
+	request, err := http.NewRequest(http.MethodPost, postURL, &b)
 	if err != nil {
 		return "", err
 	}
+	request.Header.Add("Content-Type", "application/json")
+
+	resp, err := cfg.Derived.HttpClient.Do(request.WithContext(ctx))
+	if err != nil {
+		return "", err
+	}
+	defer resp.Body.Close()
 
 	// Error if the status isn't OK
 	if resp.StatusCode != http.StatusOK {
@@ -112,11 +127,11 @@ func CheckAssociation(
 	if err != nil {
 		return false, "", "", err
 	}
-	resp, err := http.DefaultClient.Do(req.WithContext(ctx))
+	resp, err := cfg.Derived.HttpClient.Do(req.WithContext(ctx))
 	if err != nil {
 		return false, "", "", err
 	}
-
+	defer resp.Body.Close()
 	var respBody struct {
 		Medium      string `json:"medium"`
 		ValidatedAt int64  `json:"validated_at"`
@@ -160,8 +175,7 @@ func PublishAssociation(creds Credentials, userID string, cfg *config.ClientAPI)
 	}
 	request.Header.Add("Content-Type", "application/x-www-form-urlencoded")
 
-	client := http.Client{}
-	resp, err := client.Do(request)
+	resp, err := cfg.Derived.HttpClient.Do(request)
 	if err != nil {
 		return err
 	}
diff --git a/setup/config/config.go b/setup/config/config.go
index b91144078..b03ac2bda 100644
--- a/setup/config/config.go
+++ b/setup/config/config.go
@@ -16,10 +16,14 @@ package config
 
 import (
 	"bytes"
+	"crypto/tls"
+	"crypto/x509"
 	"encoding/pem"
+	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
+	"net/http"
 	"net/url"
 	"path/filepath"
 	"regexp"
@@ -97,6 +101,9 @@ type Derived struct {
 		Params map[string]interface{} `json:"params"`
 	}
 
+	// Used for request to identity server
+	HttpClient *http.Client
+
 	// Application services parsed from their config files
 	// The paths of which were given above in the main config file
 	ApplicationServices []ApplicationService
@@ -289,6 +296,26 @@ func (config *Dendrite) Derive() error {
 		return err
 	}
 
+	if config.ClientAPI.CustomCaPath != "" {
+		// Add custom CA cert
+		rootCAs, err := x509.SystemCertPool()
+		if err != nil {
+			return err
+		}
+		certs, err := ioutil.ReadFile(config.ClientAPI.CustomCaPath)
+		if err != nil {
+			return err
+		}
+		if ok := rootCAs.AppendCertsFromPEM(certs); !ok {
+			return errors.New("failed to append custom certificate")
+		}
+		trConfig := &tls.Config{
+			RootCAs: rootCAs,
+		}
+		tr := &http.Transport{TLSClientConfig: trConfig}
+		config.Derived.HttpClient = &http.Client{Transport: tr}
+	}
+
 	return nil
 }
 
diff --git a/setup/config/config_clientapi.go b/setup/config/config_clientapi.go
index 9341d5081..067dbdebf 100644
--- a/setup/config/config_clientapi.go
+++ b/setup/config/config_clientapi.go
@@ -11,6 +11,9 @@ type ClientAPI struct {
 	Matrix  *Global  `yaml:"-"`
 	Derived *Derived `yaml:"-"` // TODO: Nuke Derived from orbit
 
+	// The path to file of custom CA certificate to be added to root CA
+	CustomCaPath string `yaml:"custom_ca_path"`
+
 	InternalAPI InternalAPIOptions `yaml:"internal_api"`
 	ExternalAPI ExternalAPIOptions `yaml:"external_api"`