A minimal gRPC credentials implementation for the HTTP basic authenti…

…cation scheme

README.md

@@ -19,4 +19,21 @@ conn, err := grpc.Dial(hostname+":443", opts...)
 Get a token from within your service handler:
 ```go
 token, err := bearer.TokenFromContext(ctx)
+```
+
+##### HTTP basic authentication (user-id and password)
+
+In your client:
+```go
+opts := []grpc.DialOption{
+    grpc.WithTransportCredentials(credentials.NewTLS(&tls.Config{})),
+    grpc.WithPerRPCCredentials(basic.NewPerRPCCredentials("your user-id", "your password")),
+}
+
+conn, err := grpc.Dial(hostname+":443", opts...)
+```
+
+Get basic auth credentials from within your service handler:
+```go
+creds, err := basic.CredentialsFromContext(ctx)
 ```

credentials/basic/basic.go

@@ -0,0 +1,53 @@
+package basic
+
+import (
+	"context"
+	"encoding/base64"
+	"fmt"
+	"strings"
+
+	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/metadata"
+)
+
+const (
+	mdKey         = "authorization"
+	mdValuePrefix = "Basic "
+)
+
+type Credentials struct {
+	UserID   string
+	Password string
+}
+
+func (c Credentials) GetRequestMetadata(ctx context.Context, uri ...string) (map[string]string, error) {
+	ri, _ := credentials.RequestInfoFromContext(ctx)
+	if err := credentials.CheckSecurityLevel(ri.AuthInfo, credentials.PrivacyAndIntegrity); err != nil {
+		return nil, fmt.Errorf("unable to transfer basic.Credentials PerRPCCredentials: %v", err)
+	}
+	return map[string]string{
+		mdKey: mdValuePrefix + base64.StdEncoding.EncodeToString([]byte(c.UserID+":"+c.Password)),
+	}, nil
+}
+
+func (c Credentials) RequireTransportSecurity() bool {
+	return true
+}
+
+func NewPerRPCCredentials(userID, password string) credentials.PerRPCCredentials {
+	return Credentials{UserID: userID, Password: password}
+}
+
+func CredentialsFromContext(ctx context.Context) (Credentials, error) {
+	var c Credentials
+	mv := metadata.ValueFromIncomingContext(ctx, mdKey)
+	if mv == nil || len(mv) == 0 {
+		return c, fmt.Errorf("basic auth credentials metadata key not found in context")
+	}
+	decodedCreds, err := base64.StdEncoding.DecodeString(strings.TrimPrefix(mv[0], mdValuePrefix))
+	if err != nil {
+		return c, err
+	}
+	c.UserID, c.Password, _ = strings.Cut(string(decodedCreds), ":")
+	return c, nil
+}