diff --git a/internal/admin/admin.go b/internal/admin/admin.go
index b8a19fb..7b33e55 100644
--- a/internal/admin/admin.go
+++ b/internal/admin/admin.go
@@ -17,6 +17,7 @@ import (
 	"strconv"
 	"strings"
 
+	"gitea.mrixs.me/Mrixs/MrixsCraft-server/internal/auth"
 	"gitea.mrixs.me/Mrixs/MrixsCraft-server/internal/config"
 	"gitea.mrixs.me/Mrixs/MrixsCraft-server/internal/database"
 )
@@ -51,7 +52,7 @@ const ctxKeyUserID ctxKey = 0
 
 func (h *Handler) auth(next http.HandlerFunc) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
-		token := extractBearer(r.Header.Get("Authorization"))
+		token := auth.ExtractBearer(r.Header.Get("Authorization"))
 		if token == "" {
 			writeError(w, http.StatusUnauthorized, "Missing authorization token")
 			return
@@ -92,13 +93,6 @@ func (h *Handler) ciToken(next http.HandlerFunc) http.HandlerFunc {
 	}
 }
 
-func extractBearer(h string) string {
-	if strings.HasPrefix(h, "Bearer ") {
-		return h[7:]
-	}
-	return ""
-}
-
 // ── Modpack CRUD ──────────────────────────────────────────────
 
 type modpackRequest struct {
diff --git a/internal/api/api.go b/internal/api/api.go
index d4c5f2e..227f33a 100644
--- a/internal/api/api.go
+++ b/internal/api/api.go
@@ -3,22 +3,37 @@ package api
 
 import (
 	"crypto/sha1"
-	"crypto/sha256"
-	"crypto/subtle"
 	"encoding/hex"
 	"encoding/json"
 	"fmt"
+	"image/png"
 	"io"
 	"net/http"
 	"os"
 	"path/filepath"
-	"strconv"
+	"strings"
 
 	"gitea.mrixs.me/Mrixs/MrixsCraft-server/internal/auth"
 	"gitea.mrixs.me/Mrixs/MrixsCraft-server/internal/config"
 	"gitea.mrixs.me/Mrixs/MrixsCraft-server/internal/database"
 )
 
+// Max skin file size: 1 MB (Minecraft skins are ~2-10 KB).
+const maxSkinSize = 1 << 20
+
+// Max cape file size: 2 MB.
+const maxCapeSize = 2 << 20
+
+// Valid Minecraft skin dimensions.
+var skinDims = []struct {
+	W, H int
+}{
+	{64, 32}, // legacy (pre-1.8)
+	{64, 64}, // modern
+	{128, 128},
+	{128, 64},
+}
+
 // Handler serves public API endpoints.
 type Handler struct {
 	db  *database.DB
@@ -36,12 +51,18 @@ func (h *Handler) RegisterRoutes(mux *http.ServeMux) {
 	mux.HandleFunc("POST /api/web/register", h.register)
 	mux.HandleFunc("POST /api/web/login", h.webLogin)
 	mux.HandleFunc("POST /api/web/profile/skin", h.uploadSkin)
+	mux.HandleFunc("POST /api/web/profile/cape", h.uploadCape)
+	mux.HandleFunc("DELETE /api/web/profile/skin", h.deleteSkin)
+	mux.HandleFunc("DELETE /api/web/profile/cape", h.deleteCape)
 
 	// Launcher endpoints.
 	mux.HandleFunc("GET /api/launcher/latest", h.launcherLatest)
 	mux.HandleFunc("GET /api/servers.json", h.serversList)
 	mux.HandleFunc("GET /api/instances/{slug}/manifest.json", h.instanceManifest)
 
+	// Profile — public read.
+	mux.HandleFunc("GET /api/web/profile/{uuid}", h.getProfile)
+
 	// Skin serving.
 	mux.HandleFunc("GET /skins/{hash}.png", h.serveSkin)
 }
@@ -87,6 +108,31 @@ type launcherLatestResponse struct {
 	IsMandatory bool             `json:"is_mandatory"`
 }
 
+type profileResponse struct {
+	UUID      string         `json:"uuid"`
+	Username  string         `json:"username"`
+	Textures  *textureInfo   `json:"textures,omitempty"`
+}
+
+type textureInfo struct {
+	SkinHash string `json:"skin_hash,omitempty"`
+	CapeHash string `json:"cape_hash,omitempty"`
+	IsSlim   bool   `json:"is_slim"`
+}
+
+// Mojang session server profile response (for game client).
+type sessionProfileResponse struct {
+	ID    string              `json:"id"`
+	Name  string              `json:"name"`
+	Props []sessionProfileProp `json:"properties"`
+}
+
+type sessionProfileProp struct {
+	Name      string `json:"name"`
+	Value     string `json:"value"`
+	Signature string `json:"signature,omitempty"`
+}
+
 type errorResponse struct {
 	Error string `json:"error"`
 }
@@ -111,6 +157,12 @@ func (h *Handler) register(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Basic email validation.
+	if !strings.Contains(req.Email, "@") || !strings.Contains(req.Email, ".") {
+		writeError(w, http.StatusBadRequest, "Invalid email address")
+		return
+	}
+
 	// Check uniqueness.
 	var exists int
 	err = h.db.Pool().QueryRow(r.Context(),
@@ -162,7 +214,7 @@ func (h *Handler) webLogin(w http.ResponseWriter, r *http.Request) {
 		req.Username,
 	).Scan(&user.ID, &user.Username, &user.PasswordHash, &user.UUID)
 
-	if err != nil || !verifyPassword(req.Password, user.PasswordHash) {
+	if err != nil || !auth.VerifyPassword(req.Password, user.PasswordHash) {
 		writeError(w, http.StatusUnauthorized, "Invalid credentials")
 		return
 	}
@@ -188,11 +240,14 @@ func (h *Handler) webLogin(w http.ResponseWriter, r *http.Request) {
 }
 
 func (h *Handler) uploadSkin(w http.ResponseWriter, r *http.Request) {
-	// TODO: authenticate via session token from header.
-	// For now, accept user_id from form (to be replaced with proper auth).
-	userID, err := strconv.Atoi(r.FormValue("user_id"))
-	if err != nil || userID == 0 {
-		writeError(w, http.StatusUnauthorized, "Authentication required")
+	userID := h.authenticateRequest(w, r)
+	if userID == 0 {
+		return
+	}
+
+	r.Body = http.MaxBytesReader(w, r.Body, maxSkinSize)
+	if err := r.ParseMultipartForm(maxSkinSize); err != nil {
+		writeError(w, http.StatusBadRequest, "Cannot parse form (max 1 MB)")
 		return
 	}
 
@@ -209,13 +264,11 @@ func (h *Handler) uploadSkin(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	// Validate PNG.
-	if len(data) < 8 || string(data[:8]) != "\x89PNG\r\n\x1a\n" {
-		writeError(w, http.StatusBadRequest, "Invalid PNG file")
+	if !isValidSkinPNG(data) {
+		writeError(w, http.StatusBadRequest, "Invalid skin: must be a valid Minecraft skin PNG (64x32, 64x64, 128x128, or 128x64)")
 		return
 	}
 
-	// Compute SHA-1 hash.
 	hash := sha1Hex(data)
 
 	// Store in CAS.
@@ -245,6 +298,124 @@ func (h *Handler) uploadSkin(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, map[string]string{"hash": hash})
 }
 
+func (h *Handler) uploadCape(w http.ResponseWriter, r *http.Request) {
+	userID := h.authenticateRequest(w, r)
+	if userID == 0 {
+		return
+	}
+
+	r.Body = http.MaxBytesReader(w, r.Body, maxCapeSize)
+	if err := r.ParseMultipartForm(maxCapeSize); err != nil {
+		writeError(w, http.StatusBadRequest, "Cannot parse form (max 2 MB)")
+		return
+	}
+
+	file, _, err := r.FormFile("cape")
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "No cape file provided")
+		return
+	}
+	defer file.Close()
+
+	data, err := io.ReadAll(file)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "Cannot read cape file")
+		return
+	}
+
+	// Validate PNG header.
+	if len(data) < 8 || string(data[:8]) != "\x89PNG\r\n\x1a\n" {
+		writeError(w, http.StatusBadRequest, "Invalid PNG file")
+		return
+	}
+
+	hash := sha1Hex(data)
+
+	// Store in skins dir alongside skins (same CAS layout).
+	destDir := filepath.Join(h.cfg.SkinsDir, hash[:2])
+	if err := os.MkdirAll(destDir, 0o755); err != nil {
+		writeError(w, http.StatusInternalServerError, "Failed to store cape")
+		return
+	}
+	dest := filepath.Join(destDir, hash+".png")
+	if err := os.WriteFile(dest, data, 0o644); err != nil {
+		writeError(w, http.StatusInternalServerError, "Failed to write cape")
+		return
+	}
+
+	// Update user profile.
+	_, err = h.db.Pool().Exec(r.Context(),
+		`INSERT INTO player_textures (user_id, cape_hash)
+		 VALUES ($1, $2)
+		 ON CONFLICT (user_id) DO UPDATE SET cape_hash = $2`,
+		userID, hash,
+	)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "Failed to update profile")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, map[string]string{"hash": hash})
+}
+
+func (h *Handler) deleteSkin(w http.ResponseWriter, r *http.Request) {
+	userID := h.authenticateRequest(w, r)
+	if userID == 0 {
+		return
+	}
+
+	_, err := h.db.Pool().Exec(r.Context(),
+		`UPDATE player_textures SET skin_hash = NULL WHERE user_id = $1`,
+		userID,
+	)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "Failed to remove skin")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, map[string]string{"status": "skin removed"})
+}
+
+func (h *Handler) deleteCape(w http.ResponseWriter, r *http.Request) {
+	userID := h.authenticateRequest(w, r)
+	if userID == 0 {
+		return
+	}
+
+	_, err := h.db.Pool().Exec(r.Context(),
+		`UPDATE player_textures SET cape_hash = NULL WHERE user_id = $1`,
+		userID,
+	)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "Failed to remove cape")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, map[string]string{"status": "cape removed"})
+}
+
+// authenticateRequest extracts and validates the Bearer token from the request,
+// returning the user ID on success or 0 on failure (having already written the error).
+func (h *Handler) authenticateRequest(w http.ResponseWriter, r *http.Request) int {
+	token := auth.ExtractBearer(r.Header.Get("Authorization"))
+	if token == "" {
+		writeError(w, http.StatusUnauthorized, "Missing authorization token")
+		return 0
+	}
+
+	var userID int
+	err := h.db.Pool().QueryRow(r.Context(),
+		`SELECT user_id FROM yggdrasil_sessions
+		 WHERE access_token = $1 AND expires_at > NOW()`,
+		token,
+	).Scan(&userID)
+	if err != nil {
+		writeError(w, http.StatusUnauthorized, "Invalid or expired token")
+		return 0
+	}
+	return userID
+}
+
 func (h *Handler) launcherLatest(w http.ResponseWriter, r *http.Request) {
 	osParam := r.URL.Query().Get("os")
 	archParam := r.URL.Query().Get("arch")
@@ -330,6 +501,39 @@ func (h *Handler) instanceManifest(w http.ResponseWriter, r *http.Request) {
 	w.Write(data)
 }
 
+func (h *Handler) getProfile(w http.ResponseWriter, r *http.Request) {
+	uuid := r.PathValue("uuid")
+	if uuid == "" {
+		writeError(w, http.StatusBadRequest, "UUID is required")
+		return
+	}
+
+	var p profileResponse
+	var skinHash, capeHash *string
+	var isSlim bool
+	err := h.db.Pool().QueryRow(r.Context(),
+		`SELECT u.uuid, u.username, pt.skin_hash, pt.cape_hash, COALESCE(pt.is_slim, false)
+		 FROM users u
+		 LEFT JOIN player_textures pt ON pt.user_id = u.id
+		 WHERE u.uuid = $1`,
+		uuid,
+	).Scan(&p.UUID, &p.Username, &skinHash, &capeHash, &isSlim)
+	if err != nil {
+		writeError(w, http.StatusNotFound, "Player not found")
+		return
+	}
+
+	if skinHash != nil || capeHash != nil {
+		p.Textures = &textureInfo{
+			SkinHash: deref(skinHash),
+			CapeHash: deref(capeHash),
+			IsSlim:   isSlim,
+		}
+	}
+
+	writeJSON(w, http.StatusOK, p)
+}
+
 func (h *Handler) serveSkin(w http.ResponseWriter, r *http.Request) {
 	hash := r.PathValue("hash")
 	if hash == "" {
@@ -359,16 +563,37 @@ func (h *Handler) serveSkin(w http.ResponseWriter, r *http.Request) {
 
 // ── Helpers ───────────────────────────────────────────────────
 
-func verifyPassword(password, hash string) bool {
-	h := sha256.Sum256([]byte(password))
-	return subtle.ConstantTimeCompare([]byte(hex.EncodeToString(h[:])), []byte(hash)) == 1
-}
-
 func sha1Hex(data []byte) string {
 	h := sha1.Sum(data)
 	return hex.EncodeToString(h[:])
 }
 
+// isValidSkinPNG checks that data is a valid PNG with accepted Minecraft skin dimensions.
+func isValidSkinPNG(data []byte) bool {
+	if len(data) < 8 || string(data[:8]) != "\x89PNG\r\n\x1a\n" {
+		return false
+	}
+
+	cfg, err := png.DecodeConfig(strings.NewReader(string(data)))
+	if err != nil {
+		return false
+	}
+
+	for _, d := range skinDims {
+		if cfg.Width == d.W && cfg.Height == d.H {
+			return true
+		}
+	}
+	return false
+}
+
+func deref(s *string) string {
+	if s == nil {
+		return ""
+	}
+	return *s
+}
+
 func writeJSON(w http.ResponseWriter, status int, v any) {
 	w.Header().Set("Content-Type", "application/json")
 	w.WriteHeader(status)
diff --git a/internal/auth/auth.go b/internal/auth/auth.go
index a39eef6..1c427a5 100644
--- a/internal/auth/auth.go
+++ b/internal/auth/auth.go
@@ -11,6 +11,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"strings"
 	"time"
 
 	"gitea.mrixs.me/Mrixs/MrixsCraft-server/internal/config"
@@ -33,6 +34,12 @@ func (h *Handler) RegisterRoutes(mux *http.ServeMux) {
 	mux.HandleFunc("POST /authserver/authenticate", h.authenticate)
 	mux.HandleFunc("POST /authserver/refresh", h.refresh)
 	mux.HandleFunc("POST /authserver/validate", h.validate)
+	mux.HandleFunc("POST /authserver/invalidate", h.invalidate)
+	mux.HandleFunc("POST /authserver/signout", h.signout)
+
+	// Session server — game client queries player skins/profile.
+	mux.HandleFunc("GET /sessionserver/session/minecraft/profile/{uuid}", h.sessionProfile)
+	mux.HandleFunc("GET /sessionserver/session/minecraft/profile/{unsigned}", h.sessionProfile)
 }
 
 // ── Request / Response types ──────────────────────────────────
@@ -81,6 +88,19 @@ type errorResponse struct {
 	ErrorMessage string `json:"errorMessage"`
 }
 
+// Session server types (Mojang-compatible).
+type sessionProfileResponse struct {
+	ID    string              `json:"id"`
+	Name  string              `json:"name"`
+	Props []sessionProfileProp `json:"properties"`
+}
+
+type sessionProfileProp struct {
+	Name      string `json:"name"`
+	Value     string `json:"value"`
+	Signature string `json:"signature,omitempty"`
+}
+
 // ── Handlers ──────────────────────────────────────────────────
 
 func (h *Handler) authenticate(w http.ResponseWriter, r *http.Request) {
@@ -104,7 +124,7 @@ func (h *Handler) authenticate(w http.ResponseWriter, r *http.Request) {
 	}
 
 	// Verify password (SHA-256 hex comparison).
-	if !verifyPassword(req.Password, user.PasswordHash) {
+	if !VerifyPassword(req.Password, user.PasswordHash) {
 		writeError(w, http.StatusUnauthorized, "Forbidden", "Invalid credentials")
 		return
 	}
@@ -233,6 +253,111 @@ func (h *Handler) validate(w http.ResponseWriter, r *http.Request) {
 	w.WriteHeader(http.StatusNoContent)
 }
 
+func (h *Handler) invalidate(w http.ResponseWriter, r *http.Request) {
+	body, err := io.ReadAll(r.Body)
+	if err != nil {
+		w.WriteHeader(http.StatusBadRequest)
+		return
+	}
+
+	var req refreshRequest
+	if err := json.Unmarshal(body, &req); err != nil {
+		w.WriteHeader(http.StatusBadRequest)
+		return
+	}
+
+	_, _ = h.db.Pool().Exec(r.Context(),
+		`DELETE FROM yggdrasil_sessions WHERE access_token = $1 AND client_token = $2`,
+		req.AccessToken, req.ClientToken,
+	)
+
+	w.WriteHeader(http.StatusNoContent)
+}
+
+func (h *Handler) signout(w http.ResponseWriter, r *http.Request) {
+	body, err := io.ReadAll(r.Body)
+	if err != nil {
+		w.WriteHeader(http.StatusBadRequest)
+		return
+	}
+
+	var req struct {
+		Username string `json:"username"`
+		Password string `json:"password"`
+	}
+	if err := json.Unmarshal(body, &req); err != nil {
+		w.WriteHeader(http.StatusBadRequest)
+		return
+	}
+
+	user, err := h.findUser(r.Context(), req.Username)
+	if err != nil || !VerifyPassword(req.Password, user.PasswordHash) {
+		w.WriteHeader(http.StatusForbidden)
+		return
+	}
+
+	_, _ = h.db.Pool().Exec(r.Context(),
+		`DELETE FROM yggdrasil_sessions WHERE user_id = $1`, user.ID,
+	)
+
+	w.WriteHeader(http.StatusNoContent)
+}
+
+// sessionProfile returns the Mojang-compatible profile for the game client.
+// URL: GET /sessionserver/session/minecraft/profile/{uuid}
+// The game client uses this to look up player textures (skin + cape).
+func (h *Handler) sessionProfile(w http.ResponseWriter, r *http.Request) {
+	uuid := r.PathValue("uuid")
+	if uuid == "" {
+		http.NotFound(w, r)
+		return
+	}
+
+	// Look up user + textures by UUID.
+	var username string
+	var skinHash, capeHash *string
+	err := h.db.Pool().QueryRow(r.Context(),
+		`SELECT u.username, pt.skin_hash, pt.cape_hash
+		 FROM users u
+		 LEFT JOIN player_textures pt ON pt.user_id = u.id
+		 WHERE u.uuid = $1`,
+		uuid,
+	).Scan(&username, &skinHash, &capeHash)
+	if err != nil {
+		http.NotFound(w, r)
+		return
+	}
+
+	// Build texture URL prefix.
+	textureBase := h.cfg.BaseURL + "/skins/"
+
+	// Build properties (Mojang format).
+	props := make([]sessionProfileProp, 0, 1)
+	texObj := make(map[string]string)
+	if skinHash != nil && *skinHash != "" {
+		texObj["skin"] = textureBase + *skinHash + ".png"
+	}
+	if capeHash != nil && *capeHash != "" {
+		texObj["cape"] = textureBase + *capeHash + ".png"
+	}
+
+	if len(texObj) > 0 {
+		texJSON, _ := json.Marshal(texObj)
+		props = append(props, sessionProfileProp{
+			Name:  "textures",
+			Value: string(texJSON),
+		})
+	}
+
+	prof := sessionProfileResponse{
+		ID:    uuid,
+		Name:  username,
+		Props: props,
+	}
+
+	writeJSON(w, http.StatusOK, prof)
+}
+
 // ── Helpers ───────────────────────────────────────────────────
 
 func (h *Handler) findUser(ctx context.Context, login string) (*database.User, error) {
@@ -247,7 +372,16 @@ func (h *Handler) findUser(ctx context.Context, login string) (*database.User, e
 	return &user, nil
 }
 
-func verifyPassword(password, hash string) bool {
+// ExtractBearer extracts the token from "Authorization: Bearer <token>" header.
+func ExtractBearer(h string) string {
+	if strings.HasPrefix(h, "Bearer ") {
+		return h[7:]
+	}
+	return ""
+}
+
+// VerifyPassword checks a plaintext password against a SHA-256 hex hash.
+func VerifyPassword(password, hash string) bool {
 	h := sha256.Sum256([]byte(password))
 	return subtle.ConstantTimeCompare([]byte(hex.EncodeToString(h[:])), []byte(hash)) == 1
 }
diff --git a/internal/database/database.go b/internal/database/database.go
index 39579b5..08e6280 100644
--- a/internal/database/database.go
+++ b/internal/database/database.go
@@ -74,14 +74,22 @@ type GlobalFile struct {
 	FileName string `db:"file_name"`
 }
 
+// PlayerTextures holds skin/cape references for a user.
+type PlayerTextures struct {
+	UserID   int    `db:"user_id"`
+	SkinHash string `db:"skin_hash"`
+	CapeHash string `db:"cape_hash"`
+	IsSlim   bool   `db:"is_slim"`
+}
+
 // LauncherRelease tracks published launcher binaries.
 type LauncherRelease struct {
-	ID         int    `db:"id"`
-	Version    string `db:"version"`
-	OS         string `db:"os"`
-	Arch       string `db:"arch"`
-	SHA256     string `db:"sha256"`
-	FilePath   string `db:"file_path"`
-	IsActive   bool   `db:"is_active"`
-	IsMandatory bool  `db:"is_mandatory"`
+	ID          int    `db:"id"`
+	Version     string `db:"version"`
+	OS          string `db:"os"`
+	Arch        string `db:"arch"`
+	SHA256      string `db:"sha256"`
+	FilePath    string `db:"file_path"`
+	IsActive    bool   `db:"is_active"`
+	IsMandatory bool   `db:"is_mandatory"`
 }